eWeek dedicated a great focus about the Adobe's announcement to open source Flex 3 SDK.
If you read the Adobe Open-Source Move Sets Showdown with Microsoft and move the second page, you'll read the opinion of a member of Gartner Group and Burton Group say that moving to open source Flex 3 is a big deal :
Mark Driver, an analyst with Gartner, called the move to open-source Flex a big deal, noting that it helps Adobe competitively against incursion by Microsoft. "I think it will help head off Silverlight and remove concerns of proprietary nature of Flex in the Web world," he said.
"Open-source co-creation is a powerful way to build a strong development community," said James Governor, founder of the RedMonk market analysis firm. "Adobe's decision to open-source the Flex SDK is a radical move which should attract a new class of developer to the platform."
Richard Monson-Haefel, an analyst with Burton Group, agreed that Adobe's plan to open-source Flex is a good idea.
Read the full Adobe Open-Source Move Sets Showdown with Microsoft article.