Got the 70-300 mm IS USM lens - haven't shot that much with it yet, but it seems like a good choice for my telephoto lens. Pictures turn out sharp even at 300mm. IS is a life-saver with the lens at longer ranges - at anything higher than 1/100 i consistently get good pictures when zoomed in despite the fact that I shake like a teenage boy confronted by DD's when taking pictures
At 70 mm I can go to 1/10.