As someone who has always heard, "Ideas are worthless without execution" and who was recently told, "Just because you have an App in the iTunes Store doesn't mean that you're not still at the idea stage" I'm going to say his idea isn't worth anything.

If I'm going to give 5% of my company to someone, it will be to my very first Dev who built V1.0 for very little money to build out his portfolio and because he liked the "idea". Without him I would never have had the opportunity that I do today.