Just remember that it's an old design, with dated menus and a somewhat clunky feel, if you're used to the 40D or newer cams - 20D or 30D and it would feel like second nature.
Give it time, play around with it a lot and you'll start to get a feel for it. I was actually really disappointed with the camera until I noticed that Lightroom did some weird things to the noise patterns and switched back to editing in DPP. Now I'm in love.
I'd been shooting with 40D's for a couple of years when I added a 5D to my collection; Had no problem adapting to it, though the LCD screen is kinda tiny.
I think you'll be fine with a 5D.