Thunderbird 1.0 RC 1 is out
On wednesday the Mozilla Group posted Thunderbird 1.0 Release Candidate 1 to their site. One thing you will notice right away is the new icons, and theme improvements.
I have been using Thunderbird since version 0.3, and I've been pretty happy with it ever since. Prior to that I had been using Outlook for several years. If your not married to Outlook (your using Microsoft Exchange Server), Thunderbird is worth a spin.