Yahoo just upgraded my web based e-mail interface to their Yahoo Beta E-Mail client. It's interface is very similar to Microsoft's Web Based Outlook interface, but a lot faster, no need for multiple windows and integrated RSS. I haven't used a thick client for my e-mail in a couple of years, and after using this interface, I see no advantage to using one at all now. This interface can be navigated as quickly or quicker than a thick client system, plus it travels with me no matter which of my 6 computers I access it from. Read here to read Mossberg's review of the interface.