Flex 2 added a neat little feature which allows you to load Runtime Shared Libraries, from other domains. And since the browser caches these libraries in theory we could all point to a central set of Flex 2 Framework RSLs and users of your application would only have to download the RSLs the first time they went to an application which used them. Before I show you how to make this work, lets talk about the caveats… First and most important, THIS IS UNSUPPORTED BY ADOBE. While the Flex team is working on a better, more permanent solution to this problem, this is really a hack and despite the fact that I am using this in my applications, neither I or Adobe warranty or support the use of this in any way. Second, since there is no failover mechanism, until we find a better home for the RSLs, if you choose to point to my hosted RSLs, your application will be at the mercy of my web server. Third, if someone hacks my web server and uploads new cracked malware RSLs, or uses a man-in-the-middle attack to replace the RSLs in flight, then you (and I) have been p0wned. Fourth, I, James Ward, may have included modified Flex framework files which do bad things, like track user behavior/input and report them back to my server. While I promise I have not done this, if you choose to use these RSLs, you are putting your trust in my promise.
So despite the caveats, I still think this hack is sufficient enough for many applications. Flex engineering is really working hard to make this work for everyone. In the mean time what is outlined here may likely help you to dramatically reduce SWF size. Read on to find out how.