Most cable tos do not allow servers. So even 128k can be better than 512k if you wanted to run a web/mail server.
I get 768k up with static ip and hosting is legal but that is relative to my area, or areas that have coverage by MCI(1.5/768) or Covad(3.0/768). Everyone has different levels of service and exp. So the cable v dsl debate has no clear winner.