I read on a couple of threads that it's a good idea to do a "media dump" of your SDHC cards often, but no information on how to do it. Does anybody know what this is and how it's done?

It's in the user manual. It's called MEDIA EMPTY. Plug the camera in using AC power. AC power MUST be used and do NOT unplug the camera during this process. Doing so will damage the camera. Follow these steps: MODE>MEDIA FORMAT>Select Card>Hold the STOP button for 5 seconds>YES>YES. After the card is finished emptying, format the card. Repeat the step for all other cards and the FMU128 Flash Drive. Failure to do this often will result in data fragments building up on the cards, resulting in less space, corrupt files that can't be recovered, and even crashing and sudden shutdown of the camera. I do this at least once a week on my cards. For my FMU128, I don't dump everything to hard drives and do a MEDIA DUMP until it's full. Hope this helps.

Thanks. I couldn't find it because I was searching for "media dump". Although in the manual it doesn't say anything about fragmented files or corruption, it's supposed to be for when you have to get rid of a card or give the card to someone else and there was important data on it. But well, it doesn't take long, so just in case I'll start doing it.