I have lost most data on my 8GB SDHC Flash Card lately. Apparently, the card got corrupted when read via USB. I tried to recover my data, but only made things worse and worse. In the end, the card could not be formatted via USB. When formatted by the N800, the card became quickly corrupted. fsck gave strange errors when run on a freshly formatted card.

I see that other users here have had similar problems, up to a point where their card became unusable.

My two cents: my cards became usable again when formatted in a digital camera (a Canon that can read SDHC). Works like a charm again. Worth a try.