It's been one year since I switched to nikon, after shooting canon for many years. I thought I would list the benefits that I've found, as well as the negatives for each side. I'm not brand loyal, as many of you already know, and I don't receive any kickbacks from either side 
First, why did I sell my canon gear at a loss and spend so much more money to buy nikon? There were three reasons.
1. the 1dm3. It was the last canon camera I bought new. I had the repairs done (I sold it before the 2nd and 3rd recall information happened) and it worked much better after the repairs but, I am a wedding photographer...the camera just did not track whites as well as it's brother (the 1ds2 that I owned) in aiservo, when a bride walked down the aisle. As far as I knew at the time, it was repaired and still did not track as well as the older camera. The 1ds2 was very good at AF but not so great at very high iso.
2. After the research I had done, and my previous experience with the M3, I decided I did not want to be an early adopter of the 5Dmk2 and there were no other canon cameras that I felt like would:
- achieve good lowlight af
- have excellent high iso in low light capabilities

So here I am a year later. And this is what I've discovered.
Nikon cameras, the new ones, really have made me very happy.
- Both the D300 and the D700 have great AF abilities.
- The D700 is the best lowlight/high iso camera I've ever used personally.
- The D300 does not perform quite as well as the D700 in high iso. However it does have very good AF in lowlight, as does the D700.
- Being able to add a grip to get fast FPS (to both these cameras) and yet remove it when one wants a light weight kit is such a bonus.
- The weather sealing on these cameras works. So does the in camera sensor cleaning. First time for me that I've had a camera a whole year and not had to clean it with even a rocket blower.
- The ability to use mf lenses from days gone by.
- The flash system, imo, is superior. Though, initially, much less user friendly. It's taken quite a while for me to learn it. LOL
- The 14-24 & the 24-70 are the best (IQ wise) zooms I've ever used.
Here are the reasons not to switch:
- Cost. Nikon lenses are significantly higher priced that canon lenses. And except for the 14-24 and the 24-70, none that I own are better (or in some cases, even equal to) their canon counterparts.
- Abysmal selection of quality primes under 200mm.
- While I listed the ability to use old MF primes as a positive, it is also a negative. Because of this compatibility, nikon has not updated their primes. They have nothing for AF FX at 1.2. Their 85 1.4 is their "cream machine" and truly is their best prime below 200mm. The other primes truly suffer from "nervous bokeh" and other than their 60 2.8 macro, I won't buy them.
- HEAVY HEAVY HEAVY lenses. There are no lightweight lens options. At least not with quality glass. If one wants a lightweight kit, you have to purchase 3rd party lenses or use manual focus.
- The 5D2 does give amazing cropping abilities. Because the D700 stops at 12mp and the only option for upgrading mp is the D3x (at a stiff $7500) that does seem a lack in the nikon camp (imo...while I know mp's aren't everything...printing large could be useful in certain circumstances).
I miss canon lenses. But, I'm still not impressed with the new canon camera offerings. I want, I need, excellent low light performance. Both in iso & af. I have that in my cameras (currently we have 2xD700 & a D300 in the house). However, compiling a kit that does (now) what my canon lenses used to do...has been difficult.
If you are thinking of switching, I would seriously consider all of the above. Choose what is important to you and then make your move, or stay, as you choose. And remember, this is just one person's opinion (based on real life usage) on switching brands.
Most of all, don't base your choice on brand. Just base it on what will serve your needs best.

