The allowance is terrible. My tier has a 200GB limit which at my 25 Mbit connection can be exceeded by less than 1 hour of usage a day.
25 Mbit can download 11 GB per hour x 30 days (1 hour per day) is 330 GB of usage in a month.
I will be sad to leave my cox internet/TV/Phone service for DSL if this becomes an issue. :(