I went to the Comcast use page and found that I was doing a combined download/upload(seed) of over 350GB in November 2010, so I checked their pricing on Business Internet, since I have internet only.
Business Internet is only $5 more then Residential Internet, with no use cap, for the same speed service, over the same cable.
The only drawback is a 1, 2 or 3 year plan, rather then month to month service.
Comcast Residential:
Comcast Customer Central (Name and password required)
Users & Settings
High-Speed Internet Data Usage
View Details
If you want to do a LOT of torrenting, especially full-time seeding, then the Business Internet is the way to go.
In uTorrent 2.20, the new Preferences "Transfer Cap" page says I was seeding 200GB and downloading 80GB over a 30 day time period.
That doesn't take into account DDLs done separate from uTorrent though.
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