Hi Buddies!
The ACE for Flex 4 is just annouced and be ready to get there soon. http://www.adobe.com/devnet/flex/articles/flex_certification.html
The Attest 3 for Flex 4 which is the best study guide and mock exam for Flex 4 certification will be ready soon from http://blog.pxldesigns.com/2010/07/attest-3-for-flex-4-ace-exam-coming-shortly/
Will update more about this topic soon...