I bought my 70-200L IS II shortly after starting out in photography, and mainly for shooting concerts. Since then I've done very few gigs as I started dabbling in street and portrait photography, and the II is great for that.
I did try some of the competing 70-200s, and the F4 in particular was an absolutely epic lens, but the ability to shoot at f2.8 without worrying about image sharpness is a winner.
It was a lot of money, but it's attached to my 50D more often than any other lens, and that's a decent sign of it's usefulness. Besides which it's a lovely lens to use, hold and feel, even before you get into its optical performance. I don't mind a heavy rig though.
Currently considering the Sigma 18-35 f1.8!
Enjoy it!