First, I shot Canon for many, many years. When I was a teen, when I was in my 20's in the military and then again in my 40's when I got into digital. I loved my XT, 30D and 40D. I started becoming disenchanted when the 50D came out and just seemed to add what Nikon already had - plus some extra MPs. After lots of research into the bodies, I sold my Canon gear and went to Nikon.
I love my D300. Period. Incredible piece of hardware.
I hate Nikon lenses. Period. Why? Two reasons: selection and price.
With Nikon, you basically have two choices (three if you count manual focus models), pro level and consumer grade. The 14-24, 24-70 and 70-200 2.8 grouping is much the holy grail of the dark side. As well it should be as it will set you back nearly $6000! For three lenses, only one of which has Nikon's answer to IS - VR. That lens, the 70-200 is also criticized often for it's faults on full-frame.
Your other choice is plastic, variable aperture consumer-grade lenses. These are 3.5 - 5.6 zooms with decent IQ, but cheap build.
Canon offers consumer grade, f4 pro and f2.8 pro series lenses. Nikon doesn't seem to grasp that strategy. In fact, most of their new releases are consumer-grade crop-format offerings! Several of the new offerings (the 50/1.4 springs to mind) offer, for the first time, internal AF motors - but have been poorly received. Pro series lenses have just not been forthcoming.
I will say that, lens for lens, it seems Nikon's consumer-grade offerings are superior to Canon's. That is matched by the price you'll pay for them, as well.
The 16-35/17-40L from Canon might be matched against the 14-24 from Nikon. The Nikon is the clear winner here, but it's nearing $2000 with the recent price increases.
The 24-70 of Canon is matched by the same range zoom from Nikon - at nearly twice the cost.
The four 70-200 offerings from Canon are matched by the single 70-200/2.8 from the Dark Side. It's shortcomings are well documented - yet it sells for nearly $2000 new. All four Canon lenses whoop this thing in terms of IQ.
The 100-400? Well, sure, Nikon has the 200-400/4! Fixed aperture, VR and 8 pounds of glass. Very highly regarded. And should be for $5000.
No 300/4IS is offered, tho an older 300/4 with AF is available. At nearly the same price as the much more modern Canon lens.
No fixed aperture f4 glass (with the exception of the 300/4) is even offered. No pro-level f4 offerings at all.
As a plus, most Nikon lenses do have a five year warranty, however.
The last thing is the used Nikon market - terrible. I'm not sure if there are fewer shooters or fewer traders, but there are certainly fewer lenses on the used circuit. And they are more expensive!
I'm just rambling on here. Am I going to sell my D300? No. My 70-300VR? No. Or the 17-55/2.8 (which is FAR superior to the like-named Canon lens) or my 105VR Macro. But man, I wish so much that Nikon would take a page from Canon and produce some real pro level lenses for less than $2k! Or maybe Canon can do the same for prosumer bodies and make a D300 of their own.
I guess I'm done here. Just pointing out the grass, while appearing greener, may prove the saying that appearances can be deceptive.