Google Desktop and its Indexer just wouldn't relax today. I suspected index corruption for a while but didn't feel like uninstalling and reinstalling as I didn't want to lose any settings.
To reset your index, shut down GDS and delete everything in this folder:
C:\Documents and Settings\ <username> \Local Settings\application data\Google\Google Desktop\ <some long number>
...except the files that start with "sidebar_*.*" and you'll be back in business when it restarts.
Now playing: MaryMary - Trouble Ain't