The Canon-Nikon debate is about as old as the companies themselves, is long, sorted, and feuled by people who have thousands, if not tens of thousands of dollars invested in either system (which tends to make people suprisingly opinionated.) The truth is quality wise both make beautiful cameras that are in reality both nearly as capable in quality. I personally shoot Nikon equipment on the ground, I could go on as to why, but it's really a subjective opinion, and not relevant here. I have a Canon D60 for in the air. Why? Despite the fact that I have a lot of Nikon glass around the canon is lighter, has a faster frame rate, larger/better buffer and has a hard electric release. I'm not enthralled with it's ease of use, features, Autofocus or metering, nor have the 10D or 20D really impressed me much in these areas, but I see them of little importance for this application. In the end you have to make a decision on what tool will best fit the job you are after, I think it's the Canon line despite my love of Nikons. People here have give very good advice as well, and McGowan is absolutely right, the camera's only job is to allow the user to do his job.
-Chris