Exclude apps from Spotlight results
Launching applications with Quicksilver the “manual” way is so fast, I’ve never even bothered assigning a keystroke for one. If you did want a keystroke, you could limit the scope so it’s not active in certain applications, or so it’s only active in certain applications.

Also note that Quicksilver will very quickly learn that when you type “it”, you want iTerm by default and not iTunes, so you won’t need to remove it from the results entirely. And unlike Spotlight, you can find iTerm2 by typing something like “trm”.