I am not a pro, but I shoot a lot of dynamic scenes. That is, I never use a tripod. I use always the SR. As pointed by Ash, the SR takes 1-2 s to get stabilised and you do need to wait for SR confirmation for the best results. This is important.
I shoot from 1/10s to 1/80000s, and I always leave SR on. I am aware of the point raised by conradj and another Pentaxian (Falconeye). My understanding of Falconeye's theory is that SR might be detrimental for a range of shutter speeds. In my case, with my K-7, I cannot see distinctively any negative effects of the SR at high shutter speeds.
Food for thoughts...