As I understand it, the NSA and other agencies have the capability of reading trace residual magnetism(is magnetism the right term??) from many many previous writes - we're talking hundreds here!
Of course such recovery techniques are pretty much James Bond type scenarios. The cost of doing that depth of recovery is ridiculously expensive.
Of course if we got our hands on Saddam Hussein's HDD you can bet your *SS that we would spare no expense to get the data off that rascal:D
But for the budget most folks are on, a little freebie software program is sufficient to cover your tracks. The program I linked to is capable of 297 overwrite passes - so unless you are a celebrity or a criminal, you'll be in pretty secure shape after using it:thumb:
and yeah, you'd be amazed what can be pulled off a formatted drive