I noticed a sudden drop in my Internet speed while running Transmission. Not only on my Ubuntu box, but other computers on the same network as well.
After some searching I found that this post. I then learned that my ISP actually does shape my Internet connection; yousee.dk – shame on you! Here I am using a torrent for downloading the latest linux distro of my choice – when all of a sudden you start regulating the service I pay for!
What I did was limiting the number of peers to download from. Also, I limited my upload speed.