You can read (and see screenshots here): http://thewpfblog.com/?p=76
There is a video preview here: http://messenger.yahoo.com/windowsvista.php
From a technical point of view, it’s front-end is done entirely in Windows Presentation Foundation (WPF), so much of the Messenger application has been re-written to take advantage of that.
In other IM-related news, a new preview for Trillian’s Astra can be seen here: http://www.ceruleanstudios.com/ap/
