Excellent post. It made me think of this post by Ev Williams : http://evhead.com/2007/12/how-to-evaluate-new-product-idea.asp

On (the lack of) obviousness, he states:

“Question: Is it clear why people should use it?

Everything is obvious once its successful. Big wins come when you can spot something before its obvious to everyone else. There are several vectors to this: 1) Is it obvious why people should use it? 2) Is it obvious how to use? 3) Is it an obviously good business?”