:no:

AJAX/JSON is an extremely cool technology - using javascript to request content from servers for display. There is absolutely know doubt in my mind that it will be an important part of rich user experiences in the future of the web.

But - it shouldn’t be used everywhere. The complexity to really make it fly is expensive. If you have a simple page, or a low traffic page, or a basic application, attempting to add the layer of javascript necessary to manage the client-server communication is probably not worth it.