I installed Thunderbird 0.8 and thought everything went well and dandy.
The trouble was that one of my email accounts actually wasn't getting the email correctly. I didn't notice this all that much as most of the email that comes through that account is either spam or mailing list messages. Until one day I wondered about the absence of the (usual) 100 or so spam messages which should have been coming down with my mail check.
I logged on to my email through it's web interface and lo and behold! - over 1200 messages greeted me!
I checked my POP3 access manually, then tried with Thunderbird again. Still no messages could be seen.
A little concerned by this, I whipped out Ethereal and started a sniff on port 110 traffic. Sure enough, Thunderbird and my email server were getting confused. Turns out that it was this bug: Bug 258077 - TB will not authenticate with POP3 server -since 20040824 and the workaround in comment number 8 worked a treat and right now I'm downloading a whole heap of email. This bug has been fixed so 0.9 should work fine.
This has got me thinking though; since I didn't seem to notice this missing account for about 10 days - perhaps I should get rid of it (and it's SPAM) altogether?