In May when the cap was first rumored, there was also buzz that Comcast might try to charge customers $15 for every 10GB they went over the limit. As far as we can tell from Comcast’s announcement and the accompanying FAQ page, that is not the case… yet, anyway. Even so, Comcast’s honesty with the 250GB cap will probably only go so far, and customers with the option to do so may end up turning to an ISP such as AT&T, Verizon, or Qwest that has the infrastructure available to offer broadband without bandwidth limits.
Most people will never come anywhere close to 250 GB, but there’s a lot of adverse reaction to this plan, mainly on the issue of Comcast making it hard for you to know how much you’ve used in the current month. You may be able to get this info from your home router, but there’s no guarantee.
Regarding the threat of heaviest users to take their business elsewhere, I;m guessing Comcast won’t miss them a whole lot.