Alan McGovern chose a compromise for MonoTorrent, using async io but processing all the results in a single thread.

The Evolution of MonoTorrent - FOSDEM 2010

http://www.youtube.com/watch?v=TbhKpeqIy8o&t=10m10s

Simplified Threading API

http://monotorrent.blogspot.com/2008/10/monotorrent-050-good...