I've been learning some Flex 4 stuff over the past week. One word... wow. Even without Catalyst, this is going to speed up my development a lot. Things like skinning a button with a complex code generated skin is now easy. I've been working on a site for my Wife's budding photography business over at: Jessica Hughes Photography
It's still a rough site, but I figure Flex 4 took me about the same amount of time to make it as it would have in Flex 3, but that includes learning about all these new features.