Quicksilver crashes on me a couple of times a week. But when it's working, it's glorious and wonderful. I think people stick with QS due to momentum and familiarity (muscle memory). I tried LaunchBar 5 for a few days and it's pretty good, very close to QS in terms of functionality, but there are slight differences in usage and plugins (social bookmarking plugin - access delicious links and tags) which keep me sticking with QS.