Uber pushes the "free market" angle. That's somewhat true, but they're setting the price. A "free-er market" would have the individual drivers setting the price, and the passenger selecting among them perhaps trading off short wait time vs. low price.
It would be interesting to see a "double auction" price mechanism/order book, i.e., potential passengers submit their bids and drivers simultaneously submit their ask prices. As a passenger, you could either take the "market" price for a ride or submit a lower bid.