To those losing their SD card contents: Google a program called Recuva, download it, and then get a microSD reader for your PC and use Recuva (after doing a "quick format" in Windows) and you can probably recover some/all of the files on the card. You can try this by mounting the card via USB from your phone, but the odds of success are lower.
If you ask me, the phone isn't properly syncing data to the FAT on the card, and any change-state (a FC, a reboot, mounting it via PC, etc) causes it to corrupt the FAT and make the files un-findable. I say un-findable because they are still there (so tools like Recuva can get them back) but the FAT is corrupted so the OS has no idea how to find them anymore. The leak has enough FC-reboots for me to make me think I'm probably not the only one, and if you had an app running that was making changes to the SD card contents and it wasnt properly synced, the next boot will result in a "wiped" sd card.
To those losing their SD card contents, I will ask again: Are you 100% sure the phone didnt reboot (possibly due to a FC that you didn't even notice) or mount/unmount the card (aka attached to PC via USB) prior to you losing your files?