This is something we've been pondering at work: What would happen if you apply a magnet good for lifting 750 kilogrammes to a hard disk (we use them for lifting rather thick sheet metal)?
I wouldn't trust that. I suggest if this is work-related and there is sensitive information at all, to use an on-site data destruction service. Actually watch the drives get crushed into dust.
I used to think that these "hard drive destruction technique" threads were merely fun and interesting, but ever since Adam Lanza's deliberate destruction of his hard drives before the Connecticut classroom murders and the murder of his mother I've realized that there can be some extremely serious repercussions to these types of discussions. For all we know he may have read some of our threads or followed some of our advice! I'm doing some serious soul-searching about it. PS: LockBox, I think your advice here is excellent. I also feel that legitimate data-destruction services would be far less likely to appeal to deranged individuals who are planning a murderous rampage.
The same can be said about pretty much any discussion about privacy, but for every bad guy covering his tracks there are millions that just want to safely dispose of an old hard drive.