Your service provider can choose the sites it will carry and the speed with which any of them are delivered.
In other words, they can charge money to websites to promptly deliver content, rendering many sites useless unless they pay. (It means small and independent sites like this one or most of the blogs you visit will slow to a crawl while Clear Channel, Disney, and Doritos' content will zip to you.)
There's also a second level where this would allow effective content blocking. Think the Christian Right folks are getting ready to write their letters to Comcast? It'll start with porn and work its way towards political content.
This is just awful, and we're going to have to depend on getting a bill through the Senate to fix it! Aarrgghh!