A new version of Thunderbird was released a couple days ago (November 14th). Here are the details from the Release Notes:
What’s New in Thunderbird 184.108.40.206
- Release Date:
- November 14, 2007
- Security Update:
- The following security issues have been fixed.
- Earlier Changes:
- For information about previous changes, please see the Thunderbird 220.127.116.11 Release Notes
- Thunderbird 2 Features:
- For an overview, please see Thunderbird 2 Features.
The Rumbling Edge has a more detailed list of notable bug fixes.
More info at Mozilla Developer Centre: Thunderbird 18.104.22.168 security and stability release now available