According to Yahoo Internet News, Time Warner is to start trialling billing some of its subscribers based on usage as opposed to a flat fee.
In the US unlimited Internet plans are common, however the ISPs are starting to struggle with the increased demands on bandwidth due to rich content downloads such as audio, video, torrents etc.
The article mentions that 5% of Time Warner users account for approximately 50% of all bandwidth usage.
Locally most ISPs bill on download caps (ie 20GB), however some offer a more unlimited service. In the US it is very common to bundle ADSL with cable TV.