If your friends have lots of Canon gear, that's definitely a factor worth considering. Nikon, of course, also has a lot of market share and seems to be making serious inroads into Canon's entry-level market with low-priced camera kits. Also, the brand new Nikon D3100 (?) has 1080p video, which has been a checkbox feature that Canon has been touting. Really, you can't go wrong either way.

Personally, I find the Nikon UI to be faster to use, and I find Nikon cameras fit better in my hand. The low-end Canon D-SLRs seem designed for people with tiny hands. The more expensive Canon's fix this, but once you get into pricier camera bodies, then really it's a totally different discussion.