“Will HTML 5 make rich Internet application (RIA) technologies such as Adobe Flash/Flex and Microsoft Silverlight obsolete? For at least the next five years, the answer is a definite "no"; inconsistent implementations of the draft HTML 5 specification and immature tooling make building HTML 5 apps that work consistently across browsers and operating systems a real challenge. Furthermore, this "either/or" scenario is driven only by vendor politics, not by developer realities. Ultimately, HTML 5 and RIA platforms will be complementary technologies, and enterprise development shops will need to invest in both approaches to deliver expressive applications that combine reach and richness.”

http://www.forrester.com/rb/Research/does_html_5_herald_end_of_ria/q/id/56768/t/2