Guys, if you intend to do functional GUI testing my company will be happy to donate a few licenses of RIATest (http://www.cogitek.com/riatest.html) to Apache Flex. It can test both Flex and HTML in a browser, works on Windows and Mac. It is a commercial tool but I think we can make it free for Flex SDK testing.
Adobe Professional Services were using RIATest internally so there must be something good in the tool. :-) I have lots of experience with this stuff and will be happy to personally lead the efforts initially and help anyone interested to get up to speed with RIATest. Let me know if this is interesting and I will look further into what can be done with licenses. Tigran.