kittyhawk :
I know of HDD utilities that can recover data that has been deleted from the recycle bin. Does zero filling a hard disk drive really make all data on it totally unrecoverable?
Define totally, and also mention if you want the drive to be usable afterwards.
If you want the drive usable you can't ever 'totally' remove the possibility of data recovery. The DOD method of wiping media is very effective in making it extremely(and I mean extremely difficult) to retrieve data. You'd need multi-million dollar pieces of equipment and a team of engineers to attempt to recover your data afterwards. However, if you need to protect some of the military's nuclear secrets then buying a new drive is safer(and required as complete destruction of the media is sometimes required).
If you need complete and total impossible data recovery destroy the drive.
Me personally, if I had some kind of data on my drive that I wanted to make sure nobody could possibly recover and I had intentions of giving it to a friend or family member, a DOD wipe is plenty safe for me. Generally speaking, nobody in their right mind is gonna spend countless hours and millions of dollars to attempt to recover your 'possible' data in an attempt to see if they caught you doing something illegal(or whatever you are trying to protect).
My piece of advice.. ALWAYS disconnect ALL drives you do not want erased. It would suck to accidentally chose the wrong one.