Are asp.net devlopers using css3,E4X, and Json yet?

[Gzk2010]

Is Json considered the better file format for loadind data via Jquery AJAX?

I am going to use it either way, but from a cutting edge stand point, is JSON looked at a more cutting edge since it loads faster.

2. And for that matter is anyone using css3 and E4X? All these seem to require the latest versions of all browsers.
Since my goal is to be cutting edge I was thinking to do some stuff in the above listed that require only the latest browser if it is detected, if not use what works in most all browsers? What are cutting edge web app developers really doing at this time?

Thanks so Much,
Adam