Magnets won't harm our hard drive. In fact, Macbooks have 2 big magnets on the lid to keep it shut when closed. When closed, the left magnet is right above the hard drive. there's also a magnet on the left side of the display bezel, supposedly to hold the apple remote.
But the strongest magnets are in your hard drive itself. Pry open a broken hard drive and get the 2 magnets out, those things are very string but necessary. The only thing that could damage your hard drive is strong changing magnetic fields, think power converter house and the like.
The magsafe magnet is actually in the Macbook itself, the power brick connector is merely a piece of metal that is attracted by the magnet. No moving magnetic fields here
PS: X-rays are harmless too.