I saw this thread... I have passed by this whole MXML thing since it started...but I have grown tired of trying to manage my own UI in as3 and heard that it manages this. Where would one go to learn some tutorials on how to use MXML and Flex/FlashBuilder? I am oldschool and have been using Flash since CS2 and Flash Develop since CS3.
When I was learning Flex, I used the Flex in a Week tutorial. I still sometimes go back and reference it.
It's a good place to start, but after you get some Flex under your belt nothing beats just trying things out!