When getting rid of my home computer, I always remove the hard drive(s). Before discarding the hard drives, I
physically destroy them by dismantling them, roughing up (with a file) the actual HD surfaces, and hammering on them a bit. Not that I'm paranoid . . .
At work, I transferred data I wanted to keep to DVDs and then used a utility (like BCWipe) to wipe the hard drive of my old computer right before our IT people issued me a new one.
A colleague's "new" laptop actually came from the division VP, who made sure to clear his computer by
deleting his confidential files. Needless to say, said colleague had a lot of "inside" information available for the next year on people's salaries, promotions, and appraisals.