Really cool. This reminds me of Bret Victor's talk where he stresses the importance of seeing the effect of your code immediately (http://vimeo.com/36579366).
It's not clear from the description but it would be great if it could immediately render whatever Core Graphics code I was writing, as I was writing it, much like this in-development tool (http://www.youtube.com/watch?v=JupqhcT4ONY) which popped up in my Twitter stream a couple days ago.