Although Comcast advertises an unlimited cable-internet use policy, many heavy downloaders have run into an invisible cap, which triggers a call from Comcast's Security Department that flags their account for excessive use. The second time this happens, you're booted altogether—under the reason of hampering connection quality for your neighbors. The number 300GB has been tossed around in forums lately as the cap Comcast uses, but it could be closer to about 90 to 150GB.
A spokesperson for the cable company said that excessive use qualifies as anybody who downloads "30,000 songs, 250,000 pictures, or 13 million emails in a month." Since it's hard to quantify emails and pictures in terms of size, we'll have to judge by songs, which are usually about 3MB to 5MB depending on how high it's encoded.
But Comcast doesn't actually tell people exactly what this cap is, leading users to sit in fear of whether or not they'll go over and be booted. Although it's mostly heavy BitTorrent users who have been subject to this, the rise of ABC, NBC, Amazon, iTunes and NetFlix video services has put regular people who really enjoy TV into the same group as well. [Gamdaily via Kotaku]