Double entries in Launchpad (Mac OSX 10.7, Lion)
Launchpad looks for applications in at least two different locations: the Applications folder in your Home directory, and the "root" Applications folder sitting in "Macintosh HD." If it sees an application in more than one place, it puts an icon on the Launchpad for each place it's in. (Try using Spotlight to see if you have more than one Address Book!)

Moving the extraneous apps out of ~/Applications should put them out of Launchpad's sight (at least, as of the next reboot).