I recently did the upgrade to Snow Leopard on my MBP. To my dismay, Quicksilver no longer worked. It terminated immediately after launch.
I found the the Beta 56a7 on here.
I also had to remove Plugins.plist and the Plugins folder from ~/Library/Application Support/Quicksilver.
I am ecstatic to report that Quicksilver is up and running again, and my Mac is happy.