Microsoft's Live.com

Since I used Microsoft's new beta portal on my Linux laptop running FireFox, I may not have had the "full experience" :-) That said, live.com looks well done: the client side Javascript is slick and the interface is simple and clean.

I was not so happy with the requirement to login with Passport (otherwise, all your customizations go away when your session ends). Anyway, I think that competition between Google, Yahoo, and Microsoft in the web application area is great. Because I mostly use Linux I use Google's and Yahoo's web applications but Microsoft has announced that they will support other platforms - I am at least trying to keep an open mind about using live.com in the future, depending on what useful functionality that they provide.