<rant>
This is lost in a sea of replies now but I'm sure pissed off Mozilla is completely losing their root mantra of fighting for the free web. Persona, Thunderbird, two critical components of a "free web": free global authentication, free email client. I'm sure next mozfest the same suits as every year will talk about how they're so proud of "keeping the web open". What a crock of crap. Firefox isn't even that good of a browser anymore.
</rant>
This is one of the reasons why iPads have stalled - pro developers can't make money, for well documented reasons. The web equivalent will be the starving of open communication, thought and creativity, leading to homogeneous noise as a poor substitute for ground-breaking content.
Mostly I think it is an effort vs reward thing. Thunderbird doesn't have the user base and doesn't have a revenue stream the way fire fox sells the search box. I wonder if anyone over there has thought about cleaning it up and selling it as a white label email client.