you found my magnet! :-D kidding it probably isnt supposed to be there. magnets cant harm anything on the motherboard unless they are conductive and cause a short. it would take a hugely powerful magnet to affect the harddrive though the case and even a floppy can only be damaged if you pressed it right on to the disk surface and moved it. but probably anything else would too by scratching the surface.
it is probably fine to keep it in the case if you really wanted to, but if it moves at all (like if you drop the case) and shorts something out it would be bad.
