Zarafa and Atmail also look pretty good and I'd love to hear from anyone who is using either of them.
I use Roundcube when I'm away from my own computer. Usermin is also very useful when testing accounts on my server, but I can't imagine using it as a primary webmail client.
That said, Gmail is so much better. If I trusted them, I'd immediately switch.
However, I feel uneasy about handing over to Google large helpings personal information, even though most of it is mundane.
When I have to use Outlook, everything seems so disorganized...
I find it much superior to Gmail. Their beta AJAX web interface has the look and feel of a full desktop mail client, and is very similar to Thunderbird. Yahoo!'s AddressGuard feature is extremely useful - Google has nothing really comparable. The only drawback is that Yahoo! does not yet offer IMAP.
I use Google for my calendar and contacts (and use the Google exchange server to sync both of these to my phone).
That's what put me over the edge from Y! to Gmail - I wanted to use an email application (Thunderbird, actually) to manage multiple email accounts. And now I'm mostly using IMAP for better accessibility
Stuck with it due to incumbency, and a vague feeling [call me paranoid] that since I already use Google for so many other things, if they could also data-mine my email, they'd know almost everything about me. I don't [knowingly] use Yahoo for anything except email.
http://lifehacker.com/software/exclusive-lifehacker-download...
Also, why aren't self-hosted options like Horde and Roundcube in this poll?