Web 3.0 is already here.
It is Flash/Flex/WPFe.
AJAX is good for certain applications, but it doesn't have the horsepower to provide the next generation user experience to web users.
Development experience - You do not have to practice voodoo to write cross browser UI anymore.
Customers - You don't have to be scared to click that link because you never know which link will take the server roundtrip.
The main reason Flash doesn't get acceptance is because of ActionScript, it would have been an entirely different story if it was support javascript. You can't blame developers for not wanting to learn yet another language ECMA or not.
The main issue with WPF/e so far is it's unsuitable to create application like Flex is.
Let us wait and see whether Adobe or Microsoft executes best this vision!