BitTorrent swarms have a deadly bite on broadband nets

[Sean Donelan]

http://www.multichannel.com/article/CA6332098.html

  The short answer: Badly. Based on the research, conducted by Terry Shaw,
  of CableLabs, and Jim Martin, a computer science professor at Clemson
  University, it only takes about 10 BitTorrent users bartering files on a
  node (of around 500) to double the delays experienced by everybody else.
  Especially if everybody else is using "normal priority" services, like
  e-mail or Web surfing, which is what tech people tend to call
  "best-effort" traffic.

Adding more network bandwidth doesn't improve the network experience of 
other network users, it just increases the consumption by P2P users. 
That's why you are seeing many universities and enterprises spending 
money on traffic shaping equipment instead of more network bandwidth.