I got this from the Comcast forums. It's from four messages posted by a Comcast tech in the topic linked below.:
http://forums.Comcast.net/thread.jspa?threadID=42887&tstart=0

    Posts: 3,241       From: moderator_jason@Comcast.net
Anon38635,

Comcast monitors the network in your area and if there is an exuberant amount of bandwidth being consumed on your node, Comcast will pick out the bandwidth hogs on that node and warn them to decrease their usage or sign up for a higher tier of service.

So basically, there is not a limit on how much bandwidth you are allowed to use and we recommend that you use the Internet for what you want without worrying about bandwidth restrictions. If your usage is found to be excessive and degrades others connected to your node, you will be given a warning first and then asked to reduce the usage within the next 30 day cycle. If usage is decreased to a nominal level, no further action is taken against the customer. But if the excessive use is continued, the account may be suspended for a few months.

Hope this answers the question but please post back if you have any additional questions.


 Posts: 3,241       From: moderator_jason@Comcast.net
     Registered: 2/17/04
   
Æñon:),

In most cases, when a customer receives this warning and opts for the higher tier of service, appropriate actions are taken to re-route traffic (i.e. split a node) to prevent the excessive bandwidth consumption. Also, in most cases, opting for a higher tier of service will mean moving to a business-class package, not just a higher tier of the residential service.


Æñon:),

These are handled on more of a case-by-case basis but we forecast the bandwidth needed for all customers on a node. Each tier of service has a different expected bandwidth that is used in this forecast. When a residential customer consistently exceeds this expected bandwidth and it causes negative impacts to the remainder of the node, this is when the warnings are triggered. When a customer receives this warning and opts in for the higher workplace service tier, their forecasted bandwidth consumption is bumped up and if necessary, a node will be split to keep the performance operating effectively for everyone connected to it.

J~Storm,

Customers are allowed to use a lot of bandwidth to play online games and other activities without running the risk of receiving one of these bandwidth abuse warnings. Those who do receive the warnings are generally running heavy downloads 24x7 and are generally exceeding a normal monthly bandwidth usage by 100-fold. These customer's usage will end up affecting hundreds of other customers attached to the same node. In order to be fair to all Comcast HSI customers paying the same price for the residential service, Comcast takes action to warn excessive bandwidth users to decrease their usage or move to the higher tiers of service so that everyone can enjoy the residential service.

Also, as WTP mentions, Comcast does not advertise the High-Speed Internet service to be unlimited. It is advertised as being fast and always on but unlimited is not included in marketing campaigns.