For the benefit of WW, I will correct the fine detail of my previous post, thusly:
"If you shoot on Canon Program mode the camera automatically tries to set shutter speed fast enough not to need IS, so you would often find yourself wondering why it is there,...."
And some camera experts advise that using IS at fast shutter speeds can actually have a negative effect on sharpness, so if you accept this advice then using a lens with IS requires some vigilance:
- is the shutter speed too slow? - use a tripod and turn IS off;
- is the shutter speed too fast? - turn IS off;
- is the shutter speed just right Goldilocks? - leave IS turned on.
My point that I love IS still stands. Not sure what WW's advice is to the OP on the need for IS when choosing a lens (post #1) though....