Rated 5 out of 5 stars

Working great on Ubuntu 11.04. 100ms in settings and in System Settings->Startup Applications make sure that you have Thunderbird (Name: Thunderbird, Command: thunderbird, Comment: Thunderbird).Makes powerfull combination with "Unity unread count and quick list" (also extension for thunderbird). That way I don't need it in tray. I also added Thunderbird Indicator 1.1 add-on (it's optional) and installed standalone app "mail notification" for sound (with poups disabled in it's options)