As most know I shoot Nikon. The reason I went with Nikon is because I can use any Nikon F-mount lens on it. It is nice to be able to get that quality "old" lens and stick it on my DSLR. That being said though, I have noticed that Canon glass seems to be less expensive in price only. Case in point 70-200 f/2.8 lens with Image stabilization, Canon=$2099 Nikon=$2397
Both are very capable in the right hands though.
Just wish I could afford that new D800