Hi Carol, if shooting sports where a fairly high shutter speed is required, ie over 1/500th IS is a waste of time and money except for the possibility of horizontal panning shots
Bear in mind that while trying to AF and capture quick moving subjects the IS can take about a second until the Gyros stop spinning, if you fire the shutter during this time there is a chance the spinning gyros can throw the AF out as there is internal movement within the lens.
Ive never seen the need to use IS unless im shooting long lenses hand held on static subjects or at very low shutter speeds of 1/60th or less
For me and what i shoot (Rugby and other field sports) IS is just an expensive folly.