Here's a shady action on the part of an ISP:

Shaw cable has, this year, begun to roll out traffic-shaping technology on their network using technology from Ellacoya, and reportedy by this Wall Street Journal article. It seems they started using this service in early 2005 in the greater Vancouver area, probably because Shaw's network is most overloaded in that market. There have been reports that they are rolling it out to Edmonton, Saskatoon, and Winnipeg. Check out the reports, there's a lot of talk.

Ellacoya's technology works by "deep packet inspection" which is a type of firewall that's super-intelligent. That is, it doesn't just know about IP and TCP or UDP ports, it can also look inside the packet and see if it's FTP, HTTP, Bittorrent, kazaa, and etc. Therefore, it's not affcted by port numbers. This technology, while impressive, is not perfect. It can mis-identify packets, and requires constant upgrades to keep track of all potential types of data traversing the internet, of which there are many, and the possibility to create a new one today exists.

The issue here isn't that the ISP is doing this; it's that they are doing it quietly, leaving customers to figure out why their service is affected. The downside is, people tend to have fewer options with local ISP's than with other vendors - leaving them fewer options to effectively punish the provider.

A caveat - there are reports that this is exaggerated, but it's still worth watching.