Same here!! One of my startups failed because we chose Flex/AIR as the development platform. Nearly tripled our development time, working around bugs in the platform.
I have 3 years doing full time Flex development. Have yet to see these problems. We deploy to Windows/Linux and Flash Player has been the closest to write once/run anywhere that we've seen. We have nothing but good things to say about Flex development.
I've been writing in ActionScript 3/Flex for more than 3 years now and I don't really understand your problems. There never was a compiler bug that completely prevented me from doing my work. There always were easy workarounds to everything. The community is huge. I could always find the answer either by reading the documentation or googling.
Sincerely, compared to C++/Qt/WxWidgets, Python/Qt, Swing and even HTML/jQuery Adobe Flex was the most productive environment for frontend and desktop development for me.
It sounds that you did not have a prior experience in Flex otherwise you would know the kinks of the platform. I would say that it was not the choice of Flex that killed your startup but the uniformed choice of a technology that you never had a prior experience with.
3 years huh? I reckon you have never worked with Flex 2/3 then? The incident I am quoting is over 4 years old and I understand things may have improved with Flex 4. Specifically the Spark library drastically improved UI performance. However for us early adapters its too little too late. A Java backend with a Swing or HTML/JS front end is the safest route to go when programming for multiple platforms.