PPK describes the three main data formats for requesting data from the server, weighing up the advantages and disadvantages. In the ensuing discussion the general feeling is that JSON is the most popular and simplest method.
Promoting responsible use of JavaScript with web standards, their mission is to bring scripting up to parity with XHTML and CSS as a useful and necessary tool for building accessible, user-centric, standards-based web sites.
Some famous names in JavaScripting are involved, including Peter-Paul Koch and Dean Edwards (of IE7 fame).