The new Hotmail interface was presented at PDC - and here is already an ArsTechnica review. The UI seems clean and nice, and BTW it uses the Atlas framework under the cover.

Speaking of e-mail, I just noticed that Yahoo also has its new Y! Mail interface in works. I am looking to the pictures right now. Interestingly, both Microsoft and Yahoo arrived to remarkably similar interfaces. The same vertical left column, the overall whiteish aspect (heritage from GMail, I guess), tab views, etc.  

P.S. Funny enough, you cannot search for strings containing the exclamation point, like the "Y! Mail" name, in [blogsearch.]google.com. Although this somewhat works in MSN and Yahoo...