Plenty of good advice in here then.
I have a Canon 400d (now superseded by the 450,500, and arguably the 550) and a selection of lenses most of which have been bought 2nd hand.
The point about menu layout is valid, I love my 400d, but like the entry level Nikons, the settings you're after are often in the menus (think ISO, shooting mode, active focus points). Some of this you learn to do very fast, some of it's much easier on newer models. When you move up to the Nikon D90 or Canon 40/50D line of "prosumer" cameras a lot more features are on external controls. Add to that, that you now usually have a "top deck" type data display on the top of the camera and things are easier to see at a glance.
When my mate Tommy finally gets another case of the gimmies and buys a 7D I will try to buy his little used, beautifully looked after 40D off him
When I hold any Canon from a 10 year old film camera I've got to a new 5D MKII I find the controls intuitive. I have to keep asking Anna & Filipe to help me with the Nikon, but a large part of that is learned behaviour, they felt the same about my Canon. Try both, one will probably feel more logical to you.
If you do know a mate with several grand's worth of Nikon/Canon lenses, by all means factor that in. People have generously lent me glass that I simply couldn't afford for the limited use I'd get from it, and it's really helped me expand what I can do with the camera.
Nikon, Canon, Sigma, Tamron etc all have their "crop sensor" lenses. These are made to suit ranges such as 18-55mm and won't fill a full 35mm frame, in many cases they won't fit to a crop-sensor body at all. So if you're planning on shooting full frame or film, consider whether the lenses you're buying will be useful on all camera bodies you might use.
Above all, enjoy the experience.
Jambo
Edit: Oh yes, and all Nikon shooters smell faintly of wee. Even People like Joe McNally and David Hobby. Fact!