Ive got Sandisk 128mb that has a "bad sector" (I guess), as when I view the content from the cam it show one slot with big *?*. No matter how I format the card, it's still there. I can still use the CF but less one pic though bec it occupies 1 slot.
if u format the card and have the OS mark the corrupted part as a bad sector, then you can still continue to safely use the card, but the card will now store less pics due to the space taken up by the bad sectors. don't use quick format though!