Things are moving in the right direction for BitTorrent. The official BitTorrent client, as well as the most popular BitTorrent client out there: uTorrent, are both closing down. In the sense of source code releases.
BitTorrent 6.0, the official mainline client based on uTorrent, was released on July 28, 2006. Unlike previous official releases, there was no corresponding source code. While it's understandable that uTorrent's code may not be released, concerns remain that the protocol may advance while leaving the open source community behind.
"Sorry, source code for BitTorrent 6.0, like the source code for uTorrent, will not be released. However, versions 5 and earlier were of course released under open source licenses, and remain available for you to modify and redistribute subject to the terms of their respective licenses."
It's true enough that earlier versions of the BitTorrent protocol are available, however considering that BitTorrent is continuously evolving, older versions offer little benefit to a forward looking developer. To many in the BitTorrent community, BitTorrent, Inc. has turned its back on the open source movement.
I never was a big fan of BT to be quite honest. First of all it's slow. It's way slower than normal, proper HTTP downloads. If you run a site with big downloads and cannot handle the load, why not partner up with companies like Akamai or CacheFly? BT is only interesting for poor people and software and movie pirates. And I was never fond of them. They're criminals. That's all they are.