I've experienced several issues with Thunderbird 3.0.1, having been a user of Thunderbird since 1.0.X days. My OS is Windows XP Home SP3. My e-mail provider is Roadrunner (servers are pop-server.twcny.rr.com and smtp-server.twcny.rr.com).
Every time I open Thunderbird, the "Migration Assistant" page is open; it doesn't seem to matter that I closed it -- it is open again the next time I turn on Thunderbird 3.0.1.
2) Any changes made to settings don't seem to "stick".
2a) I once again had to delete 3 very old nntp server accounts that I haven't used in quite some time. I kept deleting them, but they kept re-appearing every time I opened Thunderbird after that. I FINALLY got rid of them by (1) manually deleting the folder they occupied, and (2) manually deleting any reference to them in user.js. Now when I open up Thunderbird again, they aren't there anymore.
2b) The first time I tried to send a new e-mail message, I got an error about secure authentication. When I looked at my account settings for the outgoing mail server, it showed my User Name filled in (my main user account for roadrunner is different from the sub-account address I use as my primary e-mail account), Secure Authentication = "No", and Connection Security = "STARTTLS, if available". The only way I was able to send a message successfully was to Edit the outgoing smtp server and uncheck "Use name and password". But the next time I turned on Thunderbird, the problem had reappeared. I finally fixed it manually by editing either user.js or prefs.js so that mail.smtpserver.smtp1.auth_method had the value of "0", and I manually deleted the line that included my username. Now when I open Thunderbird up again, I can send an e-mail without having to first change the Account Settings all over again.
This is the buggiest version of Thunderbird that I have ever installed.