Just to add a datapoint, I recently rented the amazing Canon 200mm f/2 IS lens. I went to Kerry Park in Seattle, and shot views of Seattle. Go here to see a wide-angle perspective, a telephoto perspective, and a crop of the detail in the telephoto shot. The wide angle shot was 5 seconds long, with the camera on a ledge for stability. The telephoto shot was handheld, and was only made possible with IS.


http://community.the-digital-picture.com/forums/t/2021.aspx?PageIndex=2


I'm a believer in IS.