I would say most of us are used to navigate information on the web by clicking and loading new pages with information as the default way to explore the information that is available. Since the loading of the new information usually is visible in the browser it gives a non-optimal user experience.
What seem to be the next big thing is to allow the user to seamless zoom in to get more information rather than reloading views.
It is natural, which is good. When you pick up a packet in the supermarket and want to know more your first choice is not to find a pamphlet about it but to read what is on the package. Today we can give that same experience using rich user experience frameworks like Microsoft Silverlight.
A concern many user have is if it is search engine friendly. As a developer this is something I shouldn’t have to worry about, too much. Rich applications over Internet is here, and they will stay. AJAX, Silverlight or Flash, it just doesn’t matter. The search engines must find a way for us developers to not have to worry about how our sites are indexed. Just explain how we can make sure it is indexed in a relevant way. A difficult task with spammers around.