What a fantastic idea! You've created not just a start-up but a social experiment. I have no idea if it'll work, but I love the idea of separating the act of tipping and the act of paying.

Do users get a reputation based on the proportion of tips they eventually pay out? Can you force users to tip (e.g. you must tip before you get to read this article, regardless of whether you're going to pay eventually).

And please make it multi-lingual! I'd love to try out a tipping-based business model, but just English won't cut it for me.

Nice to see another great idea in the winter batch, btw!