[cheatdeath]

I recently went through the same thing – building my own simple BitTorrent client, mostly just due to curiosity about how the protocol works. There were some tricky parts, most of which are outlined in this but I found the underlying concept so simple. I guess simplicity is a requirement for scale and resilience.

I wrote up my adventure too: http://seanjoflynn.com/research/bittorrent.html