The idea will likely die a quick death, especially now that the new Time Warner Cable/Road Runner spinoff company started charging per GB of bandwidth used this month without warning.
The industry is looking at them as a way into the future, so it might become fairly common.
Edit - I just learned that those who use a secondary service attached to Time Warner (such as Earthlink) won't have to pay Time Warner's new additional prices. So if you use Time Warner, you can simply switch to Earthlink and pay less while using the same exact infrastructure as you do now. You don't even need to change your cable modem.