I don't think anyone have ever demonstrated the ability to recover data after a few overwrites on any modern harddisk. The entire concept of "residual" magnetism that you can reliably measure sounds ridicules to an engineer.
AFAIK no-one has ever demonstrated the ability to recover data after a single overwrite. Someone offered a prize for such recovery, back in 2008 [1] which was never claimed (although the prize was only of symbolic value).
I don't want to sound like a conspiracy theorist, but if I was a 3 letter agency with infinite resources (so also no need to claim any prizes, no matter how much tempting they can be) and succeeded in recovering data that way, I would never tell anyone. Doing so would reveal what I can do, and by extension send the message "next time do a multiple pass wipe" which in the end would reveal what I cannot do.
Considering that brilliant physicists and engineers have private access to state of the art technology, I find it highly unlikely that NSA/FBI/CIA/??? have figured out how to do this, but no one else have.
