Thunderbird 0.9 is now out! New features include:
* Saved Search Folders
Saved Search Folders display messages based on previously set search criteria. For example, instead of filtering messages into a new folder, you could create a Saved Search Folder that lists all the messages received from a certain person over the past 30 days.
* Message Grouping
You can now group messages in a folder by attributes such as date, sender, priority or a custom label.
Get it from the Thunderbird home page.