Firstly, you are probably expecting that if some users pay more, you pay less. That would only make sense. But it's not likely to go down like that. ISPs don't make a lot of money being a dumb pipe for bits. No, it's the premium services you see in all in-one-providers like Comcast. High internet usage is just something else they want to monetize. It isn't about giving you a better experience, it's about how to cash in. The argument is that higher usage is forcing more upgrades. But where are they? Why am I still getting my internet through copper wires coming into my house? Where's the fiber? Recently, The New York Times wrote about how the largest ISP in Japan upgraded customers to 100Mb/s internet. In case you're wondering, the average speed in the US is 6.2Mb/s. How much did it cost for the Japanese upgrade? About $20 per home. Now take another look at your bill and decide if they should be charging you more for your measly 6 megabits.
Above: Your possible future
The second reason you're screwing yourself by not objecting to this bunk, is that the future of entertainment is online. Already we see this starting with the likes of Hulu and the new Youtube "Shows" section. I will wager that most people are smart enough to work Hulu. But how many of them can reliably monitor their bandwidth? How many even know the difference between bits and bytes? It's a great opportunity for ISPs to nickle and dime their way to a big payday.
As technology changes, we'll all want more bandwidth. If we let these companies start doing this now, it won't stop. It will become part of the business model, and we won't be able to go back. Right now, streaming video is a fairly low bitrate. In the future, however, we will expect HD streaming to be more common. A 1080p video stream uses about 1.25MB/second. That works out to about 4.4GB per hour of content. If you have a 40GB cap like Time Warner was trying to pull, you could watch a little over 9 hours of content per MONTH. That's if you do nothing else. This is where things are headed content-wise. Those that have bundled cable packages especially are fighting tooth and nail against it.
If we give our tacit approval to this now, they won't stop. We already have to complain to get faster speeds, do we really want to have to fight on another front to keep our caps high enough that we can enjoy internet innovation? Your call.