If your shutter speeds are in the 8/EFL to 1/EFL range, you would benefit from IS. If they're slower than 8/EFL, you need IS and more aperture, a camera with better/higher ISO capability, a tripod, or a combination of the above. If they're faster than 1/EFL, you won't benefit from IS.

I have the old model 2.8 IS. When I zoom to 200, I almost always drop to f/4 so I don't get the mushy corners.