I love JSON for use in JavaScript functionality. It's easier, faster and just better to use than XML in the same scenarios.

The only problem with it, is it's a hassle to format properly sometimes. Especially if you're dealing with dynamic data on the server side.

Well Thomas Frank has now put together a JSON Editor. It runs online or you can download a copy to run locally.

http://www.thomasfrank.se/json_editor.html