Quicksilver is no doubt THE App that's must have for any keyboard ninja using Mac. Please share your [power] tips on new addons, triggers and plugins that you use.
If you're using Quicksilver just as a launcher I recommend checking out "Google Quick Search Box" (http://www.google.com/quicksearchbox/).
[Holywar mode on]
Quick silver is NOT the app that's must have for any keyboard ninja using Mac since Spotlight works like a charm.
Quicksilver was good on 10.3 as there were no Spotlight :).
[Holywar mode off]