After reading this hint about the Exposé blob, and after messing with the size of the blob, I thought of a devious little prank to pull on an unsuspecting person.
Before enabling the Exposé blob, go into /System -> Library -> Core Services, and control click on Dock, and choose Show Package contents. Then open Contents -> Resources, and replace the file wvousfloat.png with a picture of your hard drive icon (using the same name), and replace wvousfloatselected.png with a picture of your hard drive icon when the drive is selected (using the same name). Then, enable the Exposé blob by following the previously mentioned hint. Finally, drag the hard-drive-shaped blob over the hard drive icon on your desktop. Now ask a friend to help diagnose the problem with your desktop hard drive icon...
[robg adds: Yea, it's a useless but simple, fun, and harmless trick for a slow winter Friday. And not too hard to diagnose and 'fix,' either, as you can drag the Exposé blob around quite easily...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20041130232907464