I wish I still had hands that were steady enough to take hand held long exposures in low light. But even back then, my keeper rate was considerably lower than shots made with a tripod or the camera otherwise 'planted' on something stable. My leaning against a wall, tree, or anything else for stability usually resulted in enough 'keepers' that I was satisfied.
These days, with 3 of my 4 lenses non-IS, I generally shoot with a shutter speed fast enough to stop camera and subject-motion caused blur. My general methodology is to crank up the ISO to the 'limit' of acceptable noise (or a little less) and adjust aperture and shutter speed as needed. Sometimes, I'm forced to shoot wide open, so DOF issues are a major consideration. Other times, I'm forced to shoot at, say, 1/30th and slower (for sufficient DOF), and therefore know I have to take maybe 20 or more shots to get a single, unblurred 'keeper'.
Bottom line, IS is nice to have, but stabilizing the camera is only part of the motion-blur cause. The other is subject movement. At slow shutter speeds, subject movement has blurred more shots for me than camera movement. Even 'posed' people at 1/30th will often move just enough to cause a blur.