For me the award goes to Moblin 2 - it absolutely rocks and I want it on my desktop (and im considering making a desktop variant which would be more suitable than the current one which is obviously designed for small screened netbooks)
Why does it rock?
If you attended the Moblin talk you already know the answer - its rocktastic design. The design that is sadly not always evident in other open source application.
Now dont get me wrong - there has always been varying degrees of successful design in Gnome, KDE and even Windows. But when it comes to the Apple standard of design, you either have it or you dont. And right now, Moblin apart, we are not even close!
With integrated web services, social desktop features and a really neat clutter based UI on top of rocktastic design - what more could you want?
(well ok besides tracker integration, vala/genie as dev language, use of favourite window manager like compiz etc etc which can all be done in a desktop variant)