I remember this method. Any one know if the older file deletion ever got fixed with 2.2.1 or later?
If you don't know what I'm talking about here's a quick rundown.
You put the .nomedia file in a folder with pictures, upon reboot all those pictures are deleted. This had something to do with them already being scanned once and them being older than the .nomedia file so instead of ignoring them it deletes them. Something along those lines (anyone have the link to the original bug report from back in '08 or '09?).
Anyway, if it hasn't been fixed you've been warned, you stand a good chance of losing all media in those folders. So backup those files - but you knew that already
The easiest remedy to this is to remove the files, rename the folder to .whatever or insert the file. Reboot. Then throw the files back onto the sdcard. That should eliminate any issues.