Just wanted to add that I've been using Flex 4 in production for more than 6 months now, and there is absolutely no reason I would ever go back to Flex 3. My first project with 4 was to convert a Flex 3 app to Flex 4, and while the transition wasn't easy, it was quite smooth. In addition, I got the chance to replace all the old buttons with nice vector button skins, which reduced file size, and I picked up a massive performance increase just by switching to spark.

He's not saying that you should debug concurrency with more threads than processors. What he is saying is that you should first work out issues not related to concurrency in threaded code, and then fix the concurrency issues using whatever method you deem correct.