First, plenty of information about this issue at StopTheCap.com
Now some information about me and my situation:
I live on the edge of the suburbs east of Rochester, where they plan on doing this cap stuff. I'm paying about $45/mo for Time Warner internet, and according to the speedtest site Frogboy used, I'm getting just under 2Mbps down and 0.3 Mbps up. The advertised rate is 10Mbps, but it's very unusual to see even half that.
Unfortunately, the only other alternative to Time Warner is dialup. Verizon is building Fios networks out from Buffalo (80 miles west) and Syracuse (70 miles east), but Rochester is served by a smaller phone company named Frontier. They provide DSL service to most of the area, but they tried unsuccessfully to impose a 5GB cap on everyone last year, and I live just outside their service area so I couldn't sign up with them anyway. I actually get my phone service from Verizon, but given the amount of open farmland between me and Syracuse, I'm not getting my hopes up for a Fios rollout here.
Regarding bandwidth usage, my router logs say that the four people in my house used a combined 50GB last month. Two of them don't do much online except websurf and trade photos with friends and other family members. The other is a teenager who plays games and watches a lot of online video, and likes to download game demos on his 360. As for myself, I own several games that get patched frequently, some of them on Impulse. I also have an eMusic subscription, and I occasionally watch videos online or download Creative Commons works from LegalTorrents.com.
One thing I would like to point out is that Time Warner already has a tiered pricing model in place, similar to the one Frogboy suggested. I have their standard service, which advertises an optimistic 10Mbps for $45/mo. There is a "Light" tier for about half the price but with a slower speed (I think 7Mbps?), and a "Turbo" tier that gives 15Mbps for $55/mo. Most people who use a lot of bandwidth are going to want the faster tier, so they're already paying more than Granny Email, who should be on the cheapest plan.
When the caps go into effect, people on the Light plan get stuck with 5GB/mo, while the Standard plan gets 20GB and Turbo users get 40GB. The speeds stay the same, so they're effectively downgrading everyone's service. Suspiciously, they're not doing it in any areas where they have actual competition.
There's so much I could say on this subject that I'm just going to stop now before this rant gets any longer. Needless to say, I am not happy.