WinSuperSite recently posted an article on the new Longhorn “Aero” UI. Now, I’m not in charge of Longhorn and so I don’t know what the final UI will look like. But I can tell you that what is posted on WSS looks nothing like the Milestone 6 version of Longhorn that I am currently running here at work. There are mockups on our corporate intranet that share similar window chrome, but (with one exception) the innards of the windows just don’t match up at all.
Summary: you’re looking at out-of-date mockups that are mostly faked.