~/Library/Application Support/Quicksilver/ (and various things inside)
~/Library/Preferences/com.blacktree.Quicksilver.plist
~/Library/Caches/Quicksilver/
If you are having trouble installing plug-ins check that the owner of
~/Library/Application Support/Quicksilver/ is the current user and not
System. If it’s not, change it and restart Quicksilver.
If you're on Tiger or Leopard be sure you're using the latest B54
(3815) version.
Howard