my posterous page starts with two slashes. They are discrete and they allow me to put JS code in a HTML comment. If you look at the source, you'll notice that when interpreted as JS it feeds a big array to window.posterousCB(). The rest is plain ond JSONP - define the global function first, and then load external cross-domain resource that runs the function with data.

As for animations - It's just a CSS transition definition and a single rule to rotate and scale an element. I created a hack that makes the CSS rule apply recursively. fun.js has some code that converts the simple html into a deeper structure.

I think someone else got the idea of _recursive CSS_ first, but it was used for drawing shapes as far as I remember.