Our forum leader is top notch, a true master of his field, able to spin up an OS + Browser in almost any permutation, in order to better empathize with his users, and kill their bugs. His name is Alex Russell, an author of Dojo Toolkit, count me a fan.
For those of you who don't know, Ajax is a foundational technology of Web 2.0, a second wave of browser bling, courtesy of a Renaissance in browser technology. Microsoft actually gets a lot of credit, for introducing an ActiveX control for interacting with a host over the wire in the background, with no click sound in user space.
The basis for dynamically changing a web page, without a reload, without an audible click, was born. Other browsers quickly followed suit, obviating reams of workarounds and hacks that had made this stuff too esoteric for 99% of developers.
I wasn't so aware of JSON before: a non-XML solution, quickly handled by eval() on the client side to create a data-rich Javascript object. I also finally installed Firebug for which Alex had plenty of high praise.