I just got a new 27" iMac and the mouse randomly freezes. It will work just fine for long periods at a time and the problem is pretty sporadic. Any ideas?
As Buysp writes, check your battery connectors. There could be some kind of interference as well from an outside or inside source. Do microwaves cause bluetooth to act funny? I know they can screw up wifi signals.
So, after getting all of the details from the user of the new iMac (it was bought for a user at work), it is only locking up if she turns her printer off.