I'm done eating my popcorn now so I'll weigh in on this topic.
IS is like Canon vs Nikon. Everyone has a different opinion so the best thing to do is try YOUR camera with YOUR lens with YOUR eyes and YOUR steady (or not) hands and use IS all of the time and then none of the time to see which shots look better.
For me, I leave it on all of the time except when on a tripod (rare). I even leave it on when using a monopod but I use mode 2 (please don't start arguments about mode 2 vs monopods vs panning).
Now everyone go out and start shooting.
mode 2 on a monopod....c'mon, you gotta be kidding me???
I did watch a youtube video recently that had the team photographer for the (my memory fails me but I believe it was Tampa Bay Rays (Major League Baseball) and he said that he and his team turn IS off because they thing the AF is faster. (shooting Canon tele's and super tele's)
anyway...this is a subject that I've read alot about recently, and it's starting to play "mind tricks" on me now. for example, I shot sports the other night and I had way too many oof shots for my liking...so I started thinking, maybe it's the IS.
as charlie brown would say....aaughhhh!