In last nights Open Iteration Meeting, Adobe gave the following dates for the Flex SDK's 3.4, 4.0 and 4.1 releases:
3.4 beta 1: June '09
3.4: August '09
4.0: Q4 '09
4.1: Q3 '10
Obviously, the further into the future you get, the more tentative these dates are :-)
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