OK. Let's be honest:
The cool thing about the way the question has been interpreted by everyone is that we get answers to two (actually several) questions!
Thanks for the info.
For me, I can only speak as to using a 24-70 as an event lens - I have rented the 24-70 f/2.8 II and the Tamron w VC. (I own the 24-105 f/4 IS).
I used the Canon 24-70 at two weddings and for a week of dance recitals/rehearsals. About 20,000 shots with the Canon (no pun intended) and a few thousand at the dance events with the Tamron.
Sorry, but the Canon was far superior - focus, color, contrast, overall image quality, usability.
I love IS - have it on most of my lenses - but did not miss it at all on the 24-70 f/2.8 II. It's a very special lens that does not require special uses.