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Free Solution

Forget LaunchpadCleaner, unless you really want to pay $5 for something that should be free. Ideally, this would be easily done in the Launchpad, but there is a free alternative.

Launchpad Control
http://chaosspace.de/launchpad-control/

It just hides the applications (or groups of applications) that you don't want to show anymore. It's not an .app, it's just a Preference pane. Works for me.
 
Launchpad.app is easy to find... it is in the Applications folder.

The question was asked in early 2011. This was when Lion was in beta and Launchpad was not in the Applications folder. Instead, it was contained inside the Dock binary and was not easily accessible unless you knew how to decompile encrypted Mac binary files.
 
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