Most people don't appreciate that 30 minutes editing Google Docs consumes 100x less data than a 30-minute Skype audio call. And the Skype call consumes 100x less than streaming a Netflix movie.
With flat-rate pricing there's no urge to conserve. But when there's a cap or penalty pricing people will almost certainly use less of everything.
We here in Australia have been subject to tiered broadband pricing since day 1 - I feel pretty comfortable in saying that whatever pricing US carriers come up with, it will be much lower than here in AU, simply because you don't need to haul most of your data thousands of KMs via undersea cables. My ISP has a range of ADSL2+ plans from AU$50/month for 150GB data through to AU$120/month for 1TB data. (There's also an entry level 30Gb for $30 plan for your grandparents)
I managed to find a real unlimited connection (here in England) so I might be a little out of touch with broadband allowances, but I think 30GB is on or above the high end of what you can get here in most places without spending a mint. Of course, they all label it as 'unlimited', which apparently is legal despite being very blantantly fraudulent advertising.
Hell, T-Mobile recently sent me some blurb trying to persuade me to replace my ADSL with their 'unlimited'* mobile broadband.
* Fair use policy applies. Bandwidth is limited to 3GB/month.
iiNet's base plan is 20Gb/month for $30: http://www.iinet.net.au/broadband/plans.html
Telstra has a 2GB/month plan for $10, but that is really just there so they can price gouge people who don't know better: http://go.bigpond.com/broadband/?ref=Net-Head-Int-Plans-Broa...
I don't know what lets T-Mobile sell 3Gb as "unlimted", but they wouldn't be allowed to call it that here.
http://adsl24.co.uk/broadband/
Look at their non-LLU packages, 30GB/month is ~£20/month. I think I'm paying for 60GB.
It's only the really huge mass-market ISPs that are offering £5-10/month packages with 1-3GB of data transfer. Once you get away from BT Broadband, Sky, and the like, you can get some decent deals.