I updated to OS X Snow Leopard yesterday. Quicksilver B54 still works with Snow Leopard, but you might run into problems with the PreferencePane.
Updating to Quicksilver B56a7 fixes this. You can get it at http://www.blacktree.com/ or use the this direct link to Quicksilver B567a.
The bad news is that you have to enable the “Show Icon in Dock” option. Quicksilver won’t work well with Spaces otherwise. Meaning that it will always open in the Space it was started in.