uTorrent is a lightweight BitTorrent client that was designed to be efficient yet offer all functoinality.
The latest release 1.8.3 for Windows can be downloaded here: http://download.utorrent.com/1.8.3/utorrent.exe
A lot of bugs have been fixed for this release, and "uTP support has been much improved to better handle mixed-mode uTP and TCP. It is not enabled by default for outgoing connections." according to the official release announce.
