There is a fascinating article in Newsweek that anyone who does anything with the web should read. It's important because it talks to a different audience (the future users) and it comes at the topic without the hype with which so many things in the "web 2.0" space seem to come bundled with. The article outlines what a lot of us already know, that the "new" web is, in the end, all about empowering the users. It's about allowing users to tag their content, connect with friends, share things and communicate in new ways. This is why the opportunity for Flash is so big.
AJAX is a great technology for building web applications. It's fast, it's standards-based and it makes ordinary looking web pages do cool things. But all of these AJAX applications still look like web pages, they just don't act like it. As the space moves forward, people are going to demand more than just uber-functional web pages. They are going to want full-fledged applications. They are going to be drawn to the kind of warm, engaging transitions that Flex makes so easy.
The Web 2.0 space has, with some exceptions, been made up of the digerati. The basic consumer doesn't care about RSS or tagging. But they do care about their data, and the fact that they don't know about RSS or tagging doesn't take away the value of those technologies. Flex allows developers to very easily create a "web experience" that people feel comfortable with and that is more "human" than current web applications. Windows Presentation Foundation does the same thing. Both Flex and WPF focus very heavily on the experience.
Right now, it's difficult to show the benefit of that to people using AJAX because AJAX does everything it needs to for the current generation of RIAs. But in the next couple of years, as more and more normal users start using the web to store data, find friends and interact with data, it won't be able to compete with WinFX and Flex because people will demand more from their web applications. If the "live web" is the internet of today, the "experiential web" will be the internet of tomorrow.