I've been using Thunderbird with the Lightning extension for quite awhile now. As an email client, especially with IMAP, I haven't found anything that beats Thunderbird. But as a calendaring/PIM/task list app, Thunderbird with Lightning sucks. I feel crippled with Lightning, not as productive as I could be, and actually *wishing* I used Outlook to try and organize my work life.
I've kept tabs on the Chandler Project here and there for awhile, too. When I've played with it, it seems to be developing into a very good Getting Things Done client. My biggest complaint is that my email is still a central part of my info work, and most of my generated things-to-do and meetings stem from email messages. But Chandler's email client sucks. I need integration between the two, but I don't want to have both Thunderbird and Chandler open at the same time. Email is still king for me, so Thunderbird wins, and I try and make do with Lightning.
So we have Thunderbird with it's strong email capabilities, and Chandler with it's strong PIM attributes. Why doesn't Mozilla scrap the Calendar/Lightning project and use the Chandler project, or why doesn't the Chandler project scrap rebuilding from scratch an email client and use an established *good* one? I don't foresee Tbird/Lightning ever coming close to the PIM abilities of Outlook anytime soon, nor do I see Chandler becoming a robust email client anytime soon. What am I missing? Why wouldn't this work?