Yes, it appears that Adobe has completely removed the Flex 3 documentation. I encountered this a few weeks ago. In case you didn't see it - have a look at this forum thread: http://forums.adobe.com/message/5943888. There are some links to downloads of the Flex 3 PDF documentation. I have not seen or heard of any mirrors or downloadable versions of the HTML version of the Flex 3 docs. Hope that helps.