A lot of that 18 billion valuation is predicated on Uber expanding beyond the "taxi" market. People are betting on them being able to use what they've learned

A lot of that 18 billion valuation is predicated on Uber expanding beyond the "taxi" market. People are betting on them being able to use what they've learned to become the king of local logistics - see their recent bike messenger expansion. And if they win the driverless car game then they could be looking at replacing much of the auto industry. Whether it's the stock market or PE or VC, investing is not a bet on what currently exists but what you think the future will hold. The numbers that exist are generally priced in already. Yes, fundraising is frothy right now but you're still talking about tons and tons of money and relatively sophisticated investors. It's not like they haven't run these same numbers.