My USB drive, which I rarely use, decided to steal the F: designation because my external drive wasn't plugged in. So when I went to commit my code changes to F:/SVN, it didn't exist anymore!

After some googling, I found that Vista has a disk management tool where you can set the letters for drives - but since I'd removed the USB drive by that point, I couldn't even find F in the list.

Rebooting fixed the problem, like always.

Ha ha, Inspiron. You got me good. But this year's best gag goes to Qualcomm:
http://www.qualcomm.com/innovation/convergence.html