I've had a few instances where workers "accidentally" had their torrents running on their laptops while at work, and the problem with our Shaw connection was if the upload bandwidth is saturated, the entire connection goes to the shitter... so everyone else in the office would have problems retrieving email or even loading up web pages.
Fortunately I had a means of figuring out which machine was causing all the traffic, so I just gave them a slap on the wrist.