This is interesting...one of the new javascript frameworks on the block (React.js, http://facebook.github.io/react/) has made use of a 'virtual dom' which basically does a diff and compares it to what was already rendered and then does minimal changes to express the new state based on that.

From what I hear (I have yet to dive into React, although I plan on it) this makes it VERY fast...because the DOM is essentially touched as little as possible directly.

I think it's a very cool idea as this could let the JIT melt together browser code with user code to one tight piece of code.

Very much aligned with React.js approach.