Facebook Digs Deeper into the Black Hole of Custom Markup
urbanhonking.com
On Facebook's new custom FBML and why markup is the wrong way to implement an API.
urbanhonking.com
If they switched from FBML to JS for providing that stuff, I would go from not being able to view my app at all until it is deployed to being able to stub out all of their calls to return test data (and even do interactive UI actions) so that I and my designer could see it pretty much exactly as it will look once live.
It's a huge difference.