I love my 7D / 17-55mm combo and yes, I use (and depend on the IS). I am ordering the 5D MkIII and will primarely use my 70-200mm IS MkII on it, but will not give up my 7D 17-55 until Canon adds IS to the 24-70.
I depend on IS (I am a senior & not as steady as I once was) and shoot a lot of events in low light. I am trying to convince myself to get the current version of the 24-70mm MkII to use with the 5D MkIII and just push the ISO to gain more shutter speed. And I am hoping the 5D MkIII's shutter is not as heavy handed as my 7D. I find myself really pushing down hard on the 7D shutter. I am glad that shutter is not the trigger on my 9mm!!