There is quite a difference in the style, crispness and feel of a photo when it's taken with either.
Just remember, if you're camera shopping to really do your research. Nikon is great because it's very sharp, very precise, and relies on you to really move slow and think about what you're shooting. But Canon is also great because it's more rapid and produces more of a depth and softness to photos. Many will say this depends on the photographer, post processing, and the lenses but having had both sides of it now I really do feel, see and find there is something quite unique in both.
Just look at photographers who use either. There is a definite feel and difference.
Needless to say, when I pick up my Canon 7D, I am completely out of sorts. The buttons are in different places and the body is so heavy. But I see some of the past photos I've taken with it and notice a style of photography that sometimes I wish I could get back to or create again.
Not to say that I don't appreciate and love my Nikon D600. It's done a lot that I wasn't able to do before and forced me to really get out of my comfort zone and for that I'm really grateful.
I think the reason I haven't sold my Canon is because I still wonder if I'll ever use it again. Of course keeping it as a back up is a good idea, but I wonder sometimes if I should've made the big jump to the Canon 5D Mark III. Then I remember, "Oh yeah, it was $1,000+ more than my Nikon."
Sometimes, ok most of the time, money is what keeps us from things but it's also what gets us out of our boxes and helps us to create some of the images we were born to.