I've known too many people who change jobs and just leave the 401k they had in their previous job with the company that is still managing the 401k for the old company. There can be (and often are) different rules for former employees that can be (and sometimes are) much more advantageous to the bank. When I left Sun the 401k moved all of the funds into a 'guaranteed interest' fund (aka a bond fund) with a 3% management fee. It was pretty egregious.