Snap, you may recall, is a search engine based on a CPA model that publishes all of its revenue data. It's open, in a financial sense. It was founded by Bill Gross of Overture/GoTo fame.
Anyways, Snap is not doing so hot:
I like Snap. I think it's a cool idea. However, the world is not beating down the door to this mousetrap. Maybe people in the online ad world just don't care about accountability yet.