Most ISPs - whether its as big as Comcast or as small as some podunk town's DSL provider, have bandwidth limits. This is especially important on cable systems, because cable Internet is a SHARED service. By shared, I mean you share bandwidth with everyone else on the same node of your provider's cable backbone network. Thus, if you're using a ton of bandwidth, you're degrading your neighbor's service. Since I don't want my service to suck because my neighbor is running a web server on his/her cable modem connection, I have no problem with ISPs charging folks who go over their bandwidth caps. These caps are generally set reasonably for most folks who use the Internet for legal purposes. Generally speaking, they aim to catch people who are downloading illegal content and/or operating servers on accounts where it is not permitted. That isn't to say that as Hollywood and the MPAA figure out that releasing media via the Internet is actually an attractive, legal option, that your bandwidth needs won't increase. Let's just hope they increase their caps as needed.
Now before you get to jumping all over me, I'll tell you how I know this. It's because I worked for several years in the broadband Internet industry. I've worked with cable and DSL services. My company quietly began the same thing--except instead of just billing them for the overage, we gave them three months to decrease usage. If they didn't, they were suspended until they upgraded their accounts to commercial (higher limits) ones. And, in our Acceptable Use Policy, we outlined the bandwidth cap(s) for all to see. So read your AUP, its probably in there.
