We have a fairly complex enterprise application that is built with Flex, BlazeDS, Java, and Spring. Version 1.8 is currently in production, and we are looking forward to delivering 2.0 before the end of the year. The Flex client by itself includes over 78,000 lines of code in 1062 files. In addition, it leverages our own corporate library SWC plus several third-party SWCs (both commercial and open-source). It was built using the Adobe Flex 4.5.1 SDK. We did not move up to 4.6 because it had bugs that broke some of our more dynamic skins.
At this point the feature list is pretty stable, and so we are thinking about performance. Some of our screens require large data sets with complex interrelationships, and algorithms that run to update those relationships (and thus redraw the visualizations) with nearly every user gesture. All in all, these screens seem to be rather obvious candidates for ActionScript workers - and so it seems time to move beyond the 4.5.1 SDK.
With no small amount of trepidation, I set up a new workspace with a fresh pull from SVN targeting the new Apache Flex 4.10.0 SDK, and made a small tweak to the compiler arguments. The result? It just worked.
After building the client with the new SDK, I put it through its paces in my local development environment. Then I deployed it to our Dev/Test server, and had a QA engineer and a software engineer perform regression testing. In the end, we found a total of 0 issues.
So, all I can say is: Kudos to the Apache Flex team. You have done a fantastic job, and deserve to be proud of what you have accomplished.