Here is an article I found that shows Comcast (my own ISP) doing things like blocking P2P traffic of their customers, etc.  Pretty interesting read …

One of the nation’s largest telecommunications companies is using a
controversial technique to cripple certain kinds of Internet traffic
traveling across its networks, says a new report from the digital
rigthts  group the Electronic Frontier Foundation in San
Francisco. 

“Comcast is essentially deploying against their own customers
techniques more typically used by malicious hackers (this is doubtless
how Comcast would characterize other parties that forged traffic to
make it appear that it came from Comcast or its subscribers,)” write
the authors of the new report. “In other words, Comcast is essentially
behaving like a telephone  operator that interrupts a phone
conversation, impersonating the voice of one party to tell the other
that this call is over, I’m hanging up.”

Read the whole article: http://blog.wired.com/27bstroke6/2007/11/comcast-using-m.html