The slider can definitely move out of place, and it is worthwhile to take a look at it any time you have dropped or otherwise jolted your N800. Resulting problems do not always point in an obvious way to the mechanical attachment of the card.

My N800 boots from the internal card, and everything seemed to be working at first when I had dropped it. After a couple of days, I found that the browser and Media Player were not saving new bookmarks, and I could not delete existing ones. It looked like a problem that could be fixed by restoring a backup. The N800 said the backup was unavailable. That was the first indication of anything wrong with the internal card. It turned out that the slider had moved. All problems were fixed by returning it into position.