JavaFX: Sun's weak go at RIA
RIA is currently populated by AJAX and Flash/Flex. Silverlight is an interesting newcomer because it provides one designer/developer experience for the all the UI offerings: Desktop, RIA, Mobile. And you can use your language of choice in a rich Design/Development experience.
Sun is attempting to get in to the RIA space with, in my opinion, a weak offering. JavaFX. Mary Jo Foly, of Microsoft Watch, I think has the most succinct analysis:
Sun's JavaFX fannouncement elt more to me like Sun's to reset Java and get the platform back on track than to break new ground.