The recommended way is to bring up the main Quicksilver interface, select the application, then drag it to the “Match Items” list. You could also drag the application(s) from a Finder window.
One problem though: Just the other day, someone pointed out that “Application Quit” triggers weren’t working. I’ve fixed it, but like I told them, I don’t know when a new release will come out that includes the fix.
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Rob McBroom