Our local consumer advocate Clark Howard, clarkhoward.com talked about this proposal on his call in radio shows.  Seems like poor infrastructure planning on their part.  Was told by a cable guy AT&T is considering same on DSL.

" Comcast to make monthly Internet use cap official
Thursday August 28, 6:21 pm ET 
Comcast to set official limit on Internet use to deter bandwidth hogs

NEW YORK (AP) -- Comcast Corp., the nation's second-largest Internet service provider, Thursday said it would set an official limit on the amount of data subscribers can download and upload each month.

On Oct. 1, the cable company will update its user agreement to say that users will be allowed 250 gigabytes of traffic per month, the company announced on its Web site.

Comcast has already reserved the right to cut off subscribers who use too much bandwidth each month, without specifying exactly what constitutes excessive use.

"We've listened to feedback from our customers who asked that we provide a specific threshold for data usage and this would help them understand the amount of usage that would qualify as excessive," the company said in a statement on its Web site.   ..............."

" .............. Comcast floated the idea of a 250 gigabyte cap in May and mentioned then that it might charge users $15 for every 10 gigabytes they go over, but the overage fee was missing in Thursday's announcement. ......."

http://biz.yahoo.com/ap/080828/comcast_internet_cap.html?.v=2