The old 5D is a heckuva buy these days, and getting better.
Just so you know, I had a 24-105 that I liked so much that when I lost it in Vegas last year (don't ask), I bought another. I considered the 24-70 F2.8 for a while, but I just couldn't get over how much I liked that 24-105 as my all-around lens. It's what sits on the camera 90% of the time.
My experience is very limited, especially compared to some of the guys on this thread, but I gotta say that a lens that throws a rookie more than an occasional bone image-wise is not a bad thing. I like the IS a LOT!