I was debating between this lens and the 24-70/2.8L. I read some reviews and understand the limitation of this lens and in the same time, many professionals choose this lens over the 24-70/2.8L because of the weight issue and the advantage of IS. I think I'd get this one and when I need to take nice portraits, I can always augment it with a fast prime.
Last week, I used it in my niece's graduation ceremony. It was held in a large indoor stadium. It doesn't have the reach to the other side of the arena. In fact, it's so big and had so many people that I didn't even know where she was. So I took some pictures at the maximum zoom. After we got home, I found her in one of the pictures when I zoomed in 100%. The faces of the people are amazing clear. It matches the resolution of 100/2.8 macro which I unwillingly sold. I had to increase the ISO to 400 and shoot at 1/60 sec, but motion blur was not a serious issue for that types of events. I also used it to take the pictures of the running athletes in the track game held next door. The pictures are very nice.
I personally don't mind the distortion at 24mm because I have a nice efs 10-22 lens for wide angle on 20D.