The amount of work you need to do is debatable, and depends on the level of perceived security you want. We found this discussion on metafilter where opinions vary on just what you need to do to completely erase data. Personally, we'd be fine with doing a low-level format(as opposed to a quick) of the hard drive and moving on, but we're not worried about anyone actually trying to get their hands on any of our data. There are also various "scrub" or "sanitize" programs that essentially perform multiple formats (this site at the University of Illinois explains this further.) Anyone have a favorite program or method of securing sensitive data?