Wesner Moise hypes Avalon, the new UI subsystem coming soon to a Longhorn near you:

If you go to PDC, and have to choose between X, Y, and Avalon, you should choose Avalon, unless you have a livelihood completely depends on X and Y. As excited as I am about Whidbey, for example, you can't build a PDC around it, and besides, you'll find out more about Whidbey from other channels and much sooner. 
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Avalon is revolutionary, rich, and complex; it's what's we have been waiting for in an API. The entire PDC could be based on it alone. You should attend the conferences about Avalon in order to appreciate and marvel at what it means. If you read about it in the Web, you might complete miss its importance.