I have commented before on this issue and a recent blog post forwarded to me has dredged up the topic again.

If you want to get rid of a drive after retiring a server or getting indicted then most of the things you can think to do to that drive will not remove the data.  You can rewrite the drive over and over, you can shatter the platters with a hammer and as we see in the link above you can even roast the drive and it is still possible to get at some of the data if not all of it.

For my money the only way to go is acid bath. If you don’t remove the surfaces of the platters then someone will figure out how to get the data.