Mozilla Thunderbird 2.0 Beta 1 has (not yet) been released. Release notes are (not yet) available. This post lists the new features and improvements in Thunderbird 2.0 Beta 1. This list encompasses almost every single known fix that went into this release. Do check out the known issues as well.
Although they say it's not yet available, the downloads are already up!"
Bugs suck. More bugs suck more. I'd rather go DOWN in bug count with the trees we spin than up, so after some regressions popped up, we're going to respin again and push the release out until next Tuesday, the 24th. This will ensure we finish playing whack-a-mole with the tree and we give the mirrors a fighting chance at getting synced up before we open the flood gates."