Last night I thought I would take a few test shots with my 70-200mm IS lens. This is a 1:1 centre crop of a handheld shot taken at 200mm, at 1/13s f/4. There is no chance I could take a picture this sharp at that shutter speed and focal length without IS. I've converted from RAW and done a little sharpening, about equal to what I would normally do on a shot to print. Also - this was not one out of a bunch of trials, but the only shot taken. The point is that it helps a lot in low light with a static subject.