Perhaps, you already know that way for 3rd parties to track file-sharing activity of the Internet users is through the IP-address. However, there's another source of data that may expose them: the peer id. (...)

BitTorrent explained that it wants to introduce a new feature whose operation would randomize peer ids in an n-hour cycle in a bid to mitigate tracking of the Internet users during the use of non-private torrents. As a result, the control will increase for the uTorrent users of their own data and activity which they ask for and are entitled to.
uTorrent Will Ensure More Privacy - ExtraTorrent.com The World's Largest BitTorrent System

Apparently this has been on 3.2.1 Beta 3 build 27941 and above for some days now. The first thing I thought is "this might leave mods and tools detectable", but it seems it wouldn't apply to private torrents, and I'm guessing they'd have the decency to make it toggleable anyway in the final release. So it's an interesting measure.