Depends on the market
This is a HUGE issue in many markets where cable effectively has no competition. However, for others, like in suburban Boston, this isn't an issue, as they have fierce competition from FIOS.
It will be interesting to see what Comcast does. It would look rather hypocritical to give certain markets unlimited, i.e. FIOS markets, while capping others, so maybe they will be forced to keep the caps off? They currently have a theoretical cap, but they even say they aren't enforcing it.