Read John Resig's blog post for more details: http://news.ycombinator.com/item?id=4382076
I came across this example (http://www.khanacademy.org/math/statistics/e/exploring_mean_...) from Khan Academy that helps students understand mean and median of a data set. (There are exercises for other summary statistics too.)
You could do exactly the same using very simple Knockout. It wouldn't be as funky, but it would be something you'd be happy to use in production.
It uses Ember.js to maintain the state of the code samples and proved to be very stable. I don't have interactive sliders on specific values, but the code is parsed and run after every character the user types. e.g. you can change the size of the squid on this page and see it reflected immediately on the right.
This is a development tool :)
For a concrete example of usefulness in games, see
I've been wanting to explore the route you took more, especially for doing even more code modification. I'd like to let users click on a number and turn it into a variable, or have a special object where members are added to the global table. You can then create controls external to the code with that table and hide the code (good for presenting after you're done coding). Looking forward to checking out your code!
my project: http://tributary.io
PS, I'm planning to implement a color picker for strings like 'rgba(200,0,234,0.4)'
EDIT: Ideally for python.
I wrote a not-as-fancy "canvas explorer" with a live updating image that you can save snapshots of.  Wrote this just yesterday to let me programmatically make images for use elsewhere (I suck at drawing tools.) I'm already enjoying the "liveness" of it and the fact that all images are remembered in localStorage. It's really cool that this is so easy to do with JS.