Unlikely - RIM have been using this idea for Blackberry's for years - all their cases all have magnets so the handset can detect when it has been "holstered", as they call it, and switches the phone to standby-mode or can be set to auto-answer/open email when removed.

I've just got a PDAair case with magnetic clasp and then found this thread. However it took a few swipes of the phone near the magnet to get the screen to switch on - I think it's fairly weak. I doubt it's going to cause me any issues, but I'm simply going to get into the habit of placing the screen on the other side of the case when I insert it, so screen towards my body. That should sort it