I have been suffering this memory card corruption issue too. Now lately my 4GB SD card that was working relatively good has become unusable.

I suspect the card is now bad because it does corrupt even when using with a PC USB card reader. I just copied a bunch of files to it and after that, without removing the card, I run disk check... and it found lots of errors and lost file fragments. Before it worked fine.

The question is that could it be that it has just wore out? I used to use that card with N800 and I had lots of MaemoMapper map files stored on it. I had formatted the card about 5 times total and copied the map files (over 20 thousand individual files) to it after each format... What I think that in that kind of use the FAT table (located in some certain memory address range) gets written each time any file is copied or deleted from the card. Once this is done some "tens of thousands times" it exceeds the life time of the memory cells located in the FAT table area.

This is just speculation from my part, but if there is someone who knows exactly how the FAT table updates are handled by the file system. Are all or some of those memory cells written each time any file change has happened?

Before I know for sure I'm not very confident starting to copy my map files to my new 8GB card... and destroy it... I'd rather use smaller and cheap card that I can afford to replace every once in a while... and use the big card for big and not frequently updated files only.