Tracker is a file indexer. It let’s you search your files wherever they are stored. Good buy, directory hierarchies! If you ever used Apple’s spotlight, you’ll know what I talk about.
Now, one cool thing is that you can integrate tracker search into the deskbar applet of your GNOME desktop. It works flawlessly. The necessary plugin handler code for the deskbar applet can be found this blog entry.
UPDATE: There is an official plugin in the tracker repository