Comcast was slowing down all Peer-to-peer traffic on it's network, which is somewhat common, but they took it a step further and starting sending packets to their customers saying the connection was reset. This made a torrent download very, very slow, like 2kb/s instead of 400 or so.
This pissed off alot of people, there are plenty of legal P2P files on the net, and Comcast was interfering with those companies ability to do business. It also affected other unintended programs, which got even more people pissed off.
This whole situation reingited a debate about network neutrality. Most users, and alot of companies, feel all traffic on the internet should be handled the same. So for example AOL shouldn't slow down traffic of a competitor, block access to certain types of content unless you buy a premium package. The ISP's want to be able to do just that, look at what type of traffic your are sending back and forth, and discriminate based on that. So Comcast might allow a movie purchased from itunes to play smoothly if they have a contract with itunes, but might make a video from Time warner go very slow.
So after the FCC got a lot of complaints, they launched an investigation. Comcast tried to scare them off by claiming the FCC had no jurisdiction. Then they apparently came to an agreement with the company that invented the bittorrent protocol, to stop sending the reset packets that cause all the issues.
They will still be slowing down some traffic, but hopefully they will do this indiscriminately of what the type of traffic is. So you might still get slowed down, but it will be because you are using 10x as much bandwidth as anyone else in your neighbourhood, not because of WHAT you are downloading.
Hopefully that is a good summary.