When thinking about what to learn and what not to learn there are two things to consider. First is marketability of a certain technology, or in other words, will new job opportunities be available to me if I learn this? From what I have seen in the industry, the market is ripe for good Flex developers right now - its a very hot technology. Flex is in a good position right now because it has essentially passed its experimental/early adopter phase and is moving on to the mainstream - but there is not a glut of programming resources available right now. The second thing to consider is: do you like programming rich web functionality? If you prefer something like deep database development, or developing enterprise integration networking services, Flex is probably not for you. But if you like putting together highly functional web apps with a cutting edge feel, Flex is definitely a technology
you should consider.
Just my 2cents
-Tony