SD Corruption specific cause for me
 

So I figured I'd make copies of all my non-music stuff on my micro-sd card. I connected the Touch to my PC, opened Storage Card, selected everything except DCIM and Music, CTRL-C, changed the explorer path to my share on my server and pasted the files.

Copy took about 5 minutes I unplugged the Touch. Notice I didn't say I closed the explorer window.

I spent about 5 minutes doing other things and wanted to copy a new cab to the touch so I connected it to my PC. Opened the Storage Card and all the folders but DCIM and Music where jibberish.

I formatted the card, test this same process again and same thing happened. I'm thinking it has something to do with an active connection between the Touch's SD card and a PC.