Edits - Nov 2011

This post was written long back in Feb 2010, since then force.com platform is drastically upgraded/changed. The illustration indicated in the post below can be achieved very easily using new platform features like Javascript Remoting.

So if you are planning to use JSON with jquery/javascript, more fun way to achieve the same is remoting, this post is a good guide to start with remoting & jquery :

Read More: https://abhinav.fyi/visualforce-salesforce-jquery-ajax-how-to/