Last thursday, Thunderbird 1.5 was released. To best new featuers are real-time spell checking (i.e. as you type.... I was so used to this on the mac, systemwide, that any program that doesn't do it on Windows is IMO broken...) and auto save...
It seems to now boldface any folder whose subfolders have unread messages, so that's nice. It doesn't show how many, but maybe that's some obsure "advanced config" parameter. It also now does auto updates, and the default setting is horrific - it will by default just download and install any updates when they become available. Lots o' confidence there in Thunderbird developer land, I suppose.
(Aside : Hopefully a different lot than the Firefox people - I added an extension from Weather.com this morning for Firefox, and after that, Firefox wouldn't come up. No window, no dialog, nothing. I tried starting by holding down shift, ctrl, etc hoping that (like many mac apps) it would start in standard-no-extentions-or-other-stuff mode. No luck. Uninstall/reinstall? Nope. Finally I noticed that it kept the extentions after the uninstall (what a nice option that would be on uninstall...) so I blew those away and now it works again... I wonder how long it would have taken your average non-professional user to figure that one out, like my father....)

