GUI for a webmail application

Hello guys,

I'm working in a small team and we're developing a webmail application
(http://www.neuridia.org). I'm about to create the GUI and I'd like to
do a quick brainstorm here

Do you like current webmail GUIs? Could you imagine the webmail
interface of your dreams? How would it be?

Ok, I'm going to help you, please have a look at these webmail GUIs:

http://www.neuridia.org/tmp/gui/samples/atmail.jpg

http://www.neuridia.org/tmp/gui/samples/gmail.jpg

http://www.neuridia.org/tmp/gui/samples/icewarp.jpg

http://www.neuridia.org/tmp/gui/samples/live.jpg

http://www.neuridia.org/tmp/gui/samples/smartermail.jpg

http://www.neuridia.org/tmp/gui/samples/yahoo.jpg

What do you like in these GUIs, and what don't you like? What about
mixing the forum GUI and the webmail GUI? Sort of having a forum
interface but to read mails? Forums and webmail have a lot of
similarities after all... I'm just thinking at loud here

Please let me know your opinion and suggestions
Thanks.