The biggest and most notable company to do such was Comcast, who decided after pressure from the FTC, their customers and other sources to settle on a cap of 250GB per month on their Internet accounts. Qwest is another nationwide ISP that has implemented similar measures, though its cap is also much larger than what Time Warner's packages offer. Time Warner does have an “in between” package planned, charging $75 for 100GB. The unlimited actually stems from a limit on how much overage they will charge, at $1 per extra gigabyte, with a maximum of $75 in extra fees.
Is this fair or acceptable? It's an important consideration - especially since Time Warner, as one of the larger ISPs in the U.S., is both a cable company and an Internet provider, and it seems the latter may be a conflict of interest. Many cable companies are concerned that Internet video services directly compete with what they offer - and when you control the medium, you can control how people view it. Is $150 extortion? Is it an excessive tab to ask?