What's being discussed right now by major software companies with main Internet Services Providers of many countries is part of differentiated services. Which means: TCP packet traversal will be given different quality of service (bandwidth, speed, etc) according to specific service agreements.
This is not so new after all, and was already applied by ISP to final customers. But now, by applying it to content providers (depending on how free those two contractors are left by the absence of democratic laws in this field), the new paradigm of two track broadband highway could undermine the principle by which every content of the net is served equally with respect to the others.
Since internet diffusion, it was possible for small companies of skilled individuals to oppose to big corporations when it came to releasing a new service to the public just because they made a better job. Just think about Youtube for instance: it was born in a garage, and became so appealing that later Google bought it. Now, what if Google videos were intrinsically (by service agreement with your ISP) streaming faster than Youtube ones? Many probably would have prefered, despite of features and of content richness, the most suitable service... I'm not saying that any of the two was better than the other, I'm just saying both made the other better because they were - until a certain point - competitors.
We are likely to go toward an unfair competition situation. It must be avoided to preserve neutrality of internet. Infact, this new shape of internet would even be penalizing for "inconvenient" third parties, which would be asked themselves to pay to remain suitable by the majority of the users.
In one word: oligopoly.