There are times when I watched some dirty movies on Quicktime Mac or clicked on file with embarrassing name to show on Preview. Then the names of those files will be recorded by quicktime and preview, and when I click and hold on the preview icon on the tray, those embarrasing names will show up. After wading thru the Mac file system I finally found what I should delete to remove those names:

Go to /Users//Library/Preferences

In that folder, delete the file com.apple.


NB: Mac OS X Lion.