It's a radical move to decide to change systems: not only is there lots to learn about lens and accessory options, and a whole new interface to get to grips with, you also have the cost and hassle of selling the old and buying the new. So the results had better be worth it when you look at handling and image output.
I thought I’d post my initial thoughts on switching as a few people have PM'd for views and it may help anyone else considering the same. I’ve always been brand neutral and bought what I considered might work best for me for the cash I had available – and I have no interest in promoting, or preference for, any brand as such. You can see all the gear I have owned in my Sig so I hope I now have a decent idea of what is possible.
Of course, beyond the rational decision there are always a few intangible elements like the 'thrill of the chase', all the research needed and the rooting out of best buys, as well as the fun of change: some hate change and some love it. I enjoy it! In many areas of life when things get too easy I can get bored, but I change only if there is good reason.
For me the lack of a reliably exceptional 50mm for the 5D, the appearance of the new D700 full-frame and the availability of the new Carl Zeiss line in Nikon mount were the reasons. Good enough? Let’s see …
All my Canon stuff below 200mm has now been sold. The 1D Mk II N and 400mm 5.6 L I am keeping for now as it is just a truly great combo for safari shooting and Nikon have nothing lens wise that gives the bang my truly stellar 5.6 L does.
Costs of switching
One of the great things about decent gear bought second hand is good resale value. Most of my Canon mount stuff was bought by acting quickly when I saw a bargain and doing the deal, or when rebates were around, so there was no risk of depreciation overall.
The Nikon stuff tends to be a tad pricier than the equivalent Canon when bought new, but some of that cost can be minimized by careful shopping around - all my replacement stuff was bought at below average retail meaning depreciation should be minimal if I sell/upgrade down-stream, same as with the Canon stuff.
I see depreciation on bodies almost as a 'rental fee' but on decent lenses I don't expect to lose much at all. The D700 of course is expensive. At release best UK price was £1998 but a week later with careful research, use of a free delivery code and a cash back link via Quidco I got it for around £200 less via purelygadgets.co.uk - an excellent retailer offering great prices, responsive service and a free extended warrantee. In the Canon line up you are looking at around £1150 for the 5D and then £2375 for the 1D Mk III.
Price will inevitably drop a bit more, but £50 here or there is not that relevant to me. The key longer term will be the 5D mk II price, but as the challenge laid down by the D700 is so stiff Canon needs to raise its game and that will reflect in an increased price over the current model. When the new 5D arrives then, as we see every time with replaced bodies, the original 5D value will drop significantly. Had I waited to sell then I would have lost another £200 or so.
So overall my change was as follows:
From ... Canon 5D, plus 17-40 4.0 L, 28-75mm 2.8, 70-200mm 4.0 IS L, 24mm 2.8, 35mm 2.0, 85mm 1.8
To ... Nikon D700, plus 18-35, 28mm 2.8 AI-S, 35mm 2.0 D, Zeiss 50mm 2.0 Makro-Planar ZF, 85mm 1.8 D, 70-300mm VR, 180mm 2.8 D
It cost me to switch, but if I factor in the profit made on the Canon gear, the projected decreased value of the 5D when the new model is released, and the added cost of an expanded set of lenses then it comes to around £650 overall, which I think is OK - your mileage on changing will vary.
So the next question revolves around whether the change was worth it beyond the financial ... some of the factors will be subjective but handling and image quality should be easy to judge given I knew my Canon stuff so well.
Handling
The first thing I consider is how my gear handles in use. If a lens or body doesn't feel right then I get rid of it. Out of the box the D700 feels right: it is a good weight, decent build, all the buttons work nicely and are well placed, the menu structure is simple to understand and operate. It is fast and pretty intuitive. It is a shooters camera because the things that need to be single click with fast, easy access are just that. The grip is good, more sticky and rubbery than the Canon and better for it, and it feels secure in hand.
However, external build is more akin to the 5D than the 1D series so that is a slight disappointment given the price and it is boxier than the Canon design, which features nice contemporary curves, so again a minus for me.
On the other hand there are lots of small, detailed touches that make it nice to use, like the way the CF cover springs open, a larger CF release button that seems easier to use, the LCD protective screen cover, the LCD screen itself which is superb and puts Canon to shame, the simple and more secure diopter adjustment, the comprehensive rear screen and viewfinder information and its super-sharp, easily readable presentation, the fantastic viewfinder just like the old film days, the ease of changing mode, focus point, WB, ISO, exposure compensation, and so on.
The D700 feels light-years ahead of the 1D Mk II N, but if you're used to and happy with the 1D style lay out then a number of these factors will likely count for less. I use the 1D control lay out no problem but it doesn't mean I necessary like it! The D700 is also much nicer than the 5D to use even if you have less need for the three hands and two feet coordination needed with that model than for the 1D's.
Overall it's a bit like driving in an old 1970’s car where the switches and controls are a little all over the place compared to a car with an ergonomically designed interior. Again, your mileage will vary on this stuff. Some like the grunt factor of an old T’Bird … I prefer the more effortless elegance of an Aston Martin. But that takes nothing from the N as an overall package – if you want to get into 1D territory then it is the best option for your money IMO.
Specifications I am not going to touch on because they are all over the internet. Suffice to say the 444 page manual pretty well covers all the features too!
Gripes
First thing I will mention is that Nikon Capture v2.0 is only supplied as a 60 day trial and then you have to cough up around £150 for a license. I use the excellent Bibble Pro for RAW and it handles D700 files already so perhaps irrelevant to me, but worth thinking about this extra cost.
If I didn’t have Bibble already then Capture would appeal. It really does seem like a great package and the shots possibly have an edge over Bibble – more time needed but I may still switch if I see a consistent and worthwhile difference. So far I don't think I have. Bibble are also very responsive and with v5.0 close to release I will wait.
The lens mount is quite tight and every time I put a lens on I wonder if I am going to break something. It is obviously good that it’s got tight tolerances here so maybe I just need to get used to it. Allied to that is the lens caps and mount are all the opposite way to what we are used to with Canon – so anti-clockwise to mount.
On the lenses with aperture rings you lock the ring at as closed down an aperture as the lens supports, so with the 35mm that I have on it at the moment I simply turn it to f22, flip the lock and it’s done as a once off action – easy as pie, but until you figure it out you get a ‘fEE’ error message and it won’t shoot, which is kinda freaky! It’s probably in the manual but who reads those?
Lenses are another irritant … partly due to price, especially of the long stuff, but perhaps also due to selection. On the latter point, possibly the only lens equivalents that are missing of note are the f4.0 L’s, but for many those are the mainstay’s in their canon arsenal. Certainly for me the 17-40mm and 70-200mm IS L 4.0 were hard to let go.
Arguably, the loss of the f4.0 L's are balanced by the super high quality wide-angles that Nikon provide: 14mm, 17-35mm and 12-24mm and we all know top of the line widey’s are a Canon weakness.
The classic pro set up of 16-35mm 2.8 L, 24-70mm 2.8 L and 70-200mm 2.8 IS are there in Nikon form via 17-35mm 2.8, 24-70mm 2.8 and 70-200mm 2.8 VR. What is missing are the more 'mid-range' L's. Price wise we’re talking for the Canon £2904 and for the Nikon £2971 – probably not huge, price of a good CP filter, but it is consistent across much of the Nikon range.
What is a bigger issue for me is the price of their longer stuff and lack of an affordable 400mm option, which is a mainstay of safari shooting: no 100-400mm IS L or 400mm 5.6 L equivalent for example. They do have 300mm 2.8 VR’s at £2850, 400mm 2.8’s at around £5400 or the hulkin’ great 200-400mm 4.0 VR at £3600! Mainly big, fast, very expensive stuff.
This is where Canon rules of course with bang per buck around their slower options being very good. Nikon just don’t go to that market segment, but you do have access to the third party stuff if you want to go that route. After my next Africa trip I will probably go 300mm 2.8 VR or 200-400mm VR and D300 for safari in full recognition that Canon offers better value here.
Finally, I don’t like the white ‘Nikon’ lettering across the flash – looks cheap and nasty. In fact, the Nikon’s have a slight ‘bling’ look about them and I personally prefer the more understated Canon look.
Performance
It is the best body I have used … end of story. The image quality is outstanding. It is just effortlessly good: feel, sharpness, ‘pop’, noise, colour accuracy, contrast, white balance, resolution, whatever way you want to look at it the D700 seems to do the job superbly well. I have tested all my new lenses too and all perform well out of the box with no focus or poor resolution issues.
So, in order top to bottom, my very first shot straight out the box, number 0001, with the Zeiss 50mm f2.0, is about the sharpest wide open 100% zero PP crop I have seen on my computer … in the original image you can clearly see the plane of focus and the fibre in the manual cover.
You need to be looking on a decent calibrated monitor ...
Finally 0007 is a quick, typical PP job with minimal sharpening and ‘auto levels’. 
Sorry they are dull test shots but this is pretty much what I always do to quickly check all is fine when I get a new lens or body. All hand-held, manual focus BTW using the focus confirm light in the viewfinder.
Conclusions
It is easy to be a fan boy and I have always avoided that. I can see the benefits of Canon and Nikon and for me it is knife edge. In system terms Canon is arguably stronger overall, but once you know the lenses you need then you can go either way and be happy if you don't mind paying the extra for most of the Nikon stuff.
I do believe the D700 is a significant step forward from the 5D, which I have always been a huge fan of, and primarily it is in handling and features; but my early opinion is that overall the shots are just a little better, like an ultra-light veil has dropped off the sensor. Stick a grip on and you get a great FPS rate too. The switch has been worth it for me. I would never say it would be worth it for everyone 
I'll add a 'high ISO' shot at some point but a couple of shots from last night seem to indicate no problems at 1600 looking at the RAW - I usually get nose bleeds shooting above 400 so I think I am pretty safe.
