Version 2.2 has been released on 04.08.2009. Current download is tbb22_20090809oss. Reproducible: Always
Version 3.0 (stable) is available even - http://www.threadingbuildingblocks.org/file.php?fid=77
Now both 2.2.013 and 3.0.20100310 in portage cvs. I masked 3.0 because it did not pass tests though, and is not the commercially aligned one. Slots are gone (sonames were identical between versions). You might have to uninstall tbb-2.1.015 if you run into conflicts.