Do the various Ripple clients leak any data about account names? If I use the official client at Ripple.com, and add someone to my contact list ... does the information "I believe that X's Ripple address is Y" get stored anywhere in unencrypted form? Is it broadcast to any central server?

I assume the answer is No, but I want to get an official confirmation. (These days many websites log a lot of user actions, my expectations from the Ripple client is that it does not).
The answer is no. Notations are stored only in your wallet which is always encrypted using your username and password.