I'm having a little fun on the side learning about Adobe Flex 2. I don't have Flex Builder 2, as it is incredibly expensive. I'm just using vi and the mxmlc compiler from the free Flex 2 SDK download. I have also downloaded the Flex Builder 2 Trial from the site, but haven't installed it yet.
Right now I'm following the "Live Docs" available online from Adobe. They're not bad, most of the examples have the Flex Builder part first and then show you the mxml source output on the next page. I've gotten along pretty well by just skipping the "Set up your project" pages.
So far, it's fun and interesting. I don't know if I'll invest in a book just yet, just to see how far I get without one.