I just had
Major file system corruption on both the Main and my 4G Sd card.
Scan disk fixed main, I lost 80% of the SD card contents. Reformatted in Windows and reloaded my books. lost all my recently Reading (multiple books in progress)
I have rolled back my Firmware to Dec , never before was it this bad.
I never (Knocking on wood) have had any corruption with USB sticks.