I couldn't agree more with your conclusions about Thunderbird...but I'm still using it.

The bug you mentioned would be annoying for sure (if it's something you're concerned about). What concerned me for the longest time was that with my install, the spam filter flat out did not work. I'd probably be using Outlook again if it weren't far more work to convert the mail database back.

Despite the fact that the email filter is working again, it's really pretty poor. Oh well, I know there's some reason I'm sticking with it...oh yes, because I don't like "labels" in GMail.