I just got a drive full message on my C: drive (I use XP). When I checked this out I saw over 100 40M files in C:\ Documents and Settings{My PC name}\Local Settings\Temp\AndroidEmulator. Deleting these freed the space. They were all dated on separate days going back a few months. I'm using the 1.0_r1 SDK which is installed on my D: drive, as is Eclipse.
I can't remember too many crashes. Perhaps these temp files are left if you don't quit the emulator normally. It might be just my setup. Anyone else seen them?