We had a hard crash of our Mac Mini the other day. It wouldn't boot after a hard power reset. Don't ask -- I'm trying to protect the innocent ;-)
My wife used to work at Apple, but I'm not a Mac man, so we brought it in to the "Genius" counter at a local Apple store. The guy was pretty helpful but he said there was no hope to recover the disk. However, I've been using computers long enough to know that this was some kind of file system error that was largely recoverable, and we had some data that wasn't yet backed up.