I rented this and didn't like it at all. At the same time I also rented a EF-S 17-55 f/2.8. I actually liked that better, maybe because the IS helped me take better shots. I have an XSi.
I really, really wanted to like the 24-70 because it was an L, and had the cool look, and I like the focal range to be a little longer vs wider. But I had to be honest with myself, and decide I personally needed the IS.
I'm one of the ones waiting for the rumored 24-70 f/2.8L II. I haven't purchased anything yet. Still holding on ...
I agree - having IS is really nice. What would you intend to use the lens for? Indoors, I tend to use my 17-55mm, but outdoors I often use my 24-105mm f/4L IS, since I can give up the stop of light and the zoom range is nice if I don't need wide angle (or if I bring along the 10-22mm as well). The 24-70mm is better for portraits with it's f/2.8, but honestly you'd be better off with a prime for that (and it's nearly break-even from a cost standpoint - 24-70 vs. 17-55 or 24-105 paired with an 85mm f/1.8 or 50mm f/1.4).
It all depends on what you are planning to use it for. Canon 24-70 f/2.8 L plus 70-200 f/2.8 L - is a typical set for wedding photogs, so yes 24-70 does get a lot of use by pros.
Personally, I would probably get it if i was working primarily outdoors (weddings, social events), but i mostly do studio work at this point, so I have plenty of light and my 24-105 f/4 L works great for me. Frankly, even for outdoor use i might prefer primes over 24-70 (if I have a second body or a second shooter, so I have enough time for proper framing with a prime).
I am no expert photographer, and yet I own the 24-70 L bougth from a fried for a very good price. It takes some really amazing pictures. I am honestly impressed with their quality and detail. But I miss IS, and I would love to trade it in for an IS version of it.