The premise seems simple and straightforward...the more Internet you use, the more you have to pay. TWC seeks to justify the new pricing levels as a means to cover the rising costs of infrastructure, although this argument may be a nonstarter, as providing upgraded speed and service may not be as expensive for Time Warner as they purport (see this article from ars technica).
I contend that widespread adoption of lower bandwidths caps, as TWC's tiered-level plan will provide, are extremely detrimental for consumers. They potentially set the entire ISP industry upon a very slippery slope, or a race to the bottom, if you will. ISP competition could lead to lower limits on bandwidth use across the board. For instance, what is to keep Comcast from lowering its current cap of 250GB/month?
Instead of saving customers money, a tiered-level bandwidth service plan could increase confusion and costs regarding monthly Internet usage. Overage charges would quickly aggregate, as bandwidth caps are exceeded. Parents will have to monitor not only what their children (and themselves) are using the Internet for, i.e. what content is being accessed, but how much Internet they are using.
Such monitoring will not be easy, because bandwidth use can be deceptive and is not a straightforward function of time. For example, surfing "traditional" html websites and checking emails, for hours at a time will typically not consume as much bandwidth as one half-hour TV show streaming from hulu (especially if you want to watch that show in Hi-Res).
Needless to say, the burden should fall on the ISP to provide customers a quick and easy way to meter bandwidth consumption. Obfuscation of bandwidth use should not be tolerated.
Additionally, many individuals will foreseeably opt into higher-level, or unlimited plans, simply because of the freedom such plans offer. Fearing overage charges, people are likely to overestimate (better safe than sorry) and end up paying for a higher tier than needed.
It would be refreshing to see an ISP step-up and move in the opposite direction. By offering an unlimited service, at a reasonable price, a provider could distinguish themselves from the TWC's of the world, and target customers with all-you-can-eat bandwidth as a major selling point.
Hopefully, ISP bandwidth caps do not become a de facto DRM for the Internet (as suggested here...). It will be interesting to see how Time Warner's tiered-level trial pans out, and what effect it may ultimately have on the future of the Internet.