Quicksilver on Snow Leopard
I've been lost and sad ever since I upgraded to Snow Leopard and couldn't run Quicksilver, so I spent a little time today poking around and found this post in Quicksilver's Google Group that talks about how you can get it to work. Looks like all you have to do is run a beta version and the post identifies a particular preference file that you should delete - I had to actually delete the entire Quicksilver folder (~/Library/Application Support/Quicksilver) in order to even get it to open. This was the trick for me. I had installed this version before, but when I fired it up, nothing would happen. I had to actually delete this entire folder before it would do anything.
But now Quicksilver is back and running on my machine and I'm very happy! Quicksilver is such an important part of my UI that I was really annoyed that I couldn't run it anymore and really disheartened to find out that Blacktree hasn't addressed this issue. In fact, from what I can tell, they aren't actively developing Quicksilver anymore and its been taken over by a group of developers that have moved it over to a GitHub repo.
If you've never used Quicksilver, I strongly encourage you to check it out - its a really nice application launcher that goes way beyond that one feature to change how you interact with your computer. If you prefer to keep your hands off the mouse and on the keyboard, you'll love Quicksilver.