AFAIR Bittorrent transmits IP-addresses in plaintext and thus hurts the privacy of any Tor-node that runs a BitTorrent client over Tor:
http://arstechnica.com/tech-policy/2011/04/not-anonymous-att...
http://arstechnica.com/tech-policy/2011/04/not-anonymous-att...
BitTorrent has to provide an IP address; it is part of the protocol. The issue is that some, most clients even if configured to use Tor will leak the true IP address of the user and not use a Tor exit's IP. Not good in any case.