I switched to LaunchBar from QS a few months back. I was running into issues with QS on Snow Leopard so gave it a shot. Definitely pleased with the results. Here are a few of the features i like:
-Search Templates -- quick ways to search resources for something. Comes with a bunch out of the box (google, amazon, etc), but it's really simple to set your own up. For example, I have the rails and ruby rdocs (from railsapi) setup as searchable from LaunchBar
-All of the OSX actions work very well, eg- "Eject All Disks". I never had much luck w/ similar actions in quicksilver
-Built in clipboard history
-Easy to launch scripts and provide input
A lot of these things were doable in QS, but i always had mixed results.
-Adam