This thread has me shaking my head. I need IS because I have a tremor. It's not terrible, but it's enough that it creates camera shake unless I'm shooting very fast shutter speeds. I use a tripod when I can, but it's not always practical. I shoot fast shutter speeds when the situation and desired image make that a good choice. Sometimes I want a slower shutter speed and then the IS really helps. I use the 5DIII which has superb high ISO capability but sometimes I want slower shutter speed because it will make a better photo.
I am glad my lenses have IS, even the 24-105.