according to one photographer i was talking to, canon is better in terms of economic value (proper use?) because lens that you buy under Canon regardless whether or not they are meant for the digital or 35mm film series or any model in those series, are interchangable so there is no need to buy seperate lenses for specific models or formats. The Nikon is more expensive in that it demands specific lenses for specific models. Other than that both brands are notable in function, it truly depends on what you're going to use the camera for. It seems a lot of individuals though, take more of a liking to Canon rather than Nikon. Good Luck!

u sure you dont have it the other way around? nikon's well known for backwards compatibility. most (if not all) nikon lenses from back in the 1980's will work for current nikon models, including DSLR's. on the contrary, canon currently uses the EF mount, which is only 20 years old. The previously used FD mount is no longer used, and therefore, owners of old canon FD mount lenses cannot use them on newer canon SLR/DSLR bodies (canon EOS line).
to the OP:
if you compare the ergonomics of the xt/xti against the d80/d200, the nikon will win out hands down. this is because the xt/xti is much smaller and made primarily of a plastic shell. a better candidate from the canon side would be the 30D/40D, which is larger and more comparable to the build/size of the nikon d80/d200.
i think ultimately, it really comes down to what you prefer to shoot more. canon makes probably the best set of prime lenses as well as sports photography lenses in the world. though nikon is no slouch, nikon's bigger advantage lies in their advanced external flash systems that canon simply cannot compete with.
whichever system you decide to get, you're getting a fine camera and the potential to use some really great gear. either way seems fine in my viewpoint. there were only 2 reasons why i went with canon.
1. my friends had lots of lenses i could borrow from time to time
2. the 30D was on rebate and was a MUCH better deal than the d80 at the time
But i do have to say.... the canon L lineup is seriously an experience people should not miss!!!