I have to teach a colleague jQuery and I think this would be a fun and quick way to learn it. I have seen brief tutorials and examples out there that use this technique: you have some content on the page, and a textarea to write and run your code to manipulate the rest of the page.
I was wondering if there is a whole site or course that uses this method. There must be one!
This is pretty much what you want – but it costs $45 –
http://www.codeschool.com/courses/jquery-air-first-flight