Quicksilver will not open on my Mac (OS 10.6). Can you help?
Here is the excerpt from Quicksilver's User Manual that should deal with your problem (note the "~" denotes your user account home directory):

The Quicksilver.app is usually in /Applications/ or ~/Applications/. When first used, the following per user files and folders are created:


~/Library/Application Support/Quicksilver/
Actions.plist - list of installed actions
Catalog.plist - the configured catalog sources
Mnemonics.plist - learned inputs, defaults and abbreviations
PlugIns.plist - the list of available plug-ins and how they are configured
Triggers.plist - the configured triggers
Caches/ - another cache folder
Indexes/ - folder of indexed items
PlugIns/ - installed plug-ins
Shelves/ - where items on the Shelf and clipboards are stored
Actions/ - not installed but create this folder to add scripts that implement actions
Templates/ - not installed but create this folder to use with the Make New... action
~/Library/Preferences/com.blacktree.Quicksilver.plist - stores various preferences and internal state
~/Library/Caches/Quicksilver/ - stores various state in binary files


To do a complete uninstall use the Uninstall Quicksilver button in the Application preferences, or remove the above files and folders.

It can also be useful to move or rename these while trouble-shooting a problem. 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.