The 1.8 branch Windows Thunderbird build which started at 19:30:00 on 2007-04-27 still hasn't finished - I think it's safe to say it's going to need some help. See the severity discussion in bug 379207 - some guidance about how to translate from tier 2 to bug severity would be quite welcome.
Rumor has it that this is "normal."
The tinderbox was reset around 15:30 that day, builds completed. It was just sitting at a shell (where someone had been running commands) when I logged in, so I ran the commands to reset the tinderbox and all appeared well.