actually the same as the nightly build 3 that came out last Saturday, anyway it’s now official:
http://www.mozillamessaging.com/en-US/about/press/archive/2009-11-24-01
http://www.mozillamessaging.com/en-US/thunderbird/early_releases/downloads/
http://www.mozillamessaging.com/en-US/thunderbird/3.0rc1/releasenotes/