Being at MAX is already beginning to be a great learning experience. I've met a few people who've never used Flex and have no idea about MXML. I just found myself spontaneously describing MXML as "HTML for the Flash platform" to a web developer from Ohio.
One of the reasons Flex has been such a "niche" thing is the licensing. When people cannot afford to pay thousands of dollars for the server license, they're just not interested in the technology. That is not to say that nobody uses Flex (it's a successful business for Macromedia), but it's nowhere near as mainstream as HTML and Flash. I'm hoping to see that change with the new licensing model.
Peter Elst has made a nice post about Flex/MXML versus the Flash IDE. Flex is not a Flash killer, it's just a much more RAD way of doing application development for the Flash platform. Flex is not an alternative to DHTML/JavaScript (a.k.a. AJAX), it's a way to enhance the user experience of web-based applications built on these technologies.
So, for those of you who're not aware of Flex and have never written a single line of MXML code, tomorrow when you get up in the morning, remind yourself to download the new Flex 2 IDE and command-line tools (for CLUEfuls like yours truly). Check out Kevin's presentation showing the new Flex Builder IDE and the Measure Map application built on "AJAX" and Flash technology. Feel free to develop and deploy as many applications as you like with the alpha version of Flex 2.