A guy I know bid on an old non-working hard drive. It was big, something like ten inches by maybe 18 inches by three inches. I asked him why he wanted it, and he said he'd show me.
A few days later, the display on my CRT started wobbling. The guy was holding a magnet a good six feet away from my monitor and rotating it slightly. Needless to say, he got it out of the hard drive. He had to use a ball joint separator to get the two magnets apart. Each one was about the size of two decks of cards, if I recall correctly.
I never found out what the strength of those magnets was. He soon made the mistake of holding one in each hand. They got too close together and in a split second they had collided, nipping off a little of the skin from his fingers in the process. I figure he's really lucky that's all that happened. I can think of a number of ways it could have been worse.
He brought in the now-stuck-together magnets and surprisingly (to me, anyway) their magnetic pull for other objects was very weak, like they were each absorbing the magnetism of the other. I asked if he was going to try to separate them, and he said no, and showed me that they were both cracked.
I think he was, too, a little.
Anyway, that's all the experience I've had with what were to me monstrously powerful magnets.