The only way that a magnet could erase data that I know of is if it is on a media that is magnetic in nature. Of course I suppose that a big enough magnet could do something but I would think that it would have to be HUGE! In general the magnet thing was based on an issue with PC's due to the magnet disks they use.
the case I got is the original case from hTC the two magnet is so powerful that I can stick the case & the phone on my frig. I have been using it for three days now since I got the case and the micro sd & the Tilt is still working. hope it's ok