No Kidding
Do we not all read the BOFH? The Geek Squad is a huge employeer of PFYs. Give most young geeks access to customers hard drive and this will happen. No amount of training or supervision will stop it (however, when they are caught, they should be disciplined according to company policy so they learn that it is not acceptable).
It is the computers owner that is responsible for make sure there isn't anything on the HD that they do not want to be seen by others.