Sloan, you probably pulled the card or USB cable out before your mp3s were finished transferring. Don't believe your OS when it says that the transfer is finished because it's usually NOT. On Linux, if you mount your card sync, it will make sure that you won't have this problem, but the transfer will appear to go slower. With async (the default), it will appear that the transfer is finished. In reality, it's just been done flushing the write to the card reader, which takes additional time to write to the card.

A good rule of thumb is to just wait an extra minute or two after the transfer appears to be complete on your computer before pulling out the cable or card. If it's a very large transfer (1GB+), give it an extra minute or so. You should have a lot less trouble then. (Since instituting this rule on myself, I haven't had a single card issue in 8 months.)

(This is not a Nokia or tablet problem. This is a flaw in the way card readers work. Nothing can be done about it.)