Tor is a distributed 'onion' network, that makes it more difficult for an adversary to track any one peer on the network. Tor also is very useful to access the 'uncensored' internet in countries such as China and Iran.
Bitcoin can run easily on the Tor network. (needs a brief howto here)
Conducting business using bitcoin-otc can be done more anonymously when directly connected to a Freenode IRC hidden service.