I have subscribed to site that are updated with the latest news, reviews, tutorials and etc. Luckily LinuxMag happen to be one of those sites. Today the newsletter that I got from LM included a review about Mozilla Thunderbird 3.0b4 (I used TB2 before reading that article). After reading the article i decided to give it a try and searched for Mozilla PPA for ubuntu to give it a try, and now after 5,6 hours of playing with TB3b4 i would say it deserves the words LM review has put on. It has new features like archive, improved gmail support, a lot better email search and view, tabs, and easy way to manage contacts.
If you use ubuntu and wanna give it a try this link will help you. Again i would say that its beta software, which in my experience is cool, may be break stuff so do make a backup of ~/.mozilla-thunderbird and then install it. If you like it, you can uninstall TB2 by:
apt-get remove --purge thunderbird
aptitude remove thunderbird
Or ofcourse your could use Add/Remove or Synaptic.