Thought I'd bring this to the attention of anyone out there who might be as thoughtless as I am.
I happened to be working on my Macbook Pro tonight and also had my iPad 2 out as well.
Without thinking i laid my iPad down on top of my open
Macbook and was surprised as the Macbook went dark for a second. I was thinking I had covered up a light sensor and still without thinking I put the iPad back down to see if it would do it again but this time my Macbook restarted on it's own and suddenly it dawned on me that i had been setting a powerful magnet down on top of my hard drive.
So far I haven't run into any corruption or data loss but I haven't actually done much on my Macbook yet.
Only time will tell if I made a major blunder or got off easy.

I don't think you did anything to it. I once set my MacBook down on one of those security demagnetizers in retail stores that are at the registers. I first hear the noise indicating if it demagnetized something or not. And was pretty scared, thinking I screwed up my then only few months old MacBook. But started it up and didn't see anything wrong with the hard drive or anything else. So if mine is okay then your iPad couldn't have screwed it up.

I was about to say that we recently had a customer put there iPhone on a security scanner on a bench next to the exit. And it shut down.

I had to do a reset of the iPhone then it came to life it did not like it at all.

I would think the RAM would be more an issue than the hard drive, or in the case of the iOS units, SSD.

I think the iOS device is safe in regards of magnets. There is some pretty good magnets in the smart cover and that doesn't hurt it.

My Macbook Pro has a serial ATA drive in it though which I was afraid might have been partially wiped but so far everything seems ok.Phew!