We've been running review board internally here and has slowly begun to replace email and bugzilla for tracking changes.  However, one usability problem we ran into is that users have to guess what a peer's login name is.  In both bugzilla and email you can either chose from a user list or from an address book.

To help ease adoption of reviewboard, we've added autocomplete on the people field against the user database.  After each keypress in the people field, we use the YUI toolkit to perform a JSON request to the server to fetch any usernames that begin with the keystrokes entered.  User entries are separated by commas.

(Updated to include autocomplete of groups as well as people)

Tested against a local instance of reviewboard using MySQL on the backend for the user table and LDAP for authentication.

Browsers tested: Safari 3.0, IE 6.0, and Firefox 2.0.