Thunderbird 1.5 was released today.
Rumbling Edge has a good list of new features in version 1.5. The main improvements are (pod|blog|zen|personal on demand)casting, phishing detection, spell check as you type and improved update mechanism.
Just installed it but it won’t load up on my system for some strange reason.
The problem I was talking to you about with the delay between clicking on my message, and it displaying in Thunderbird, was not a problem with the mail app. I found out it was because of my anti-virus program, avast!, that the delay was happening. 1.5 seems to me, a bit faster.