That makes it a large bubble. Market cap in and of itself is useless. How long do you see customers staying loyal after VC money stops subsidising every ride?
It will be interesting to see what happens when subsidies end. There are likely to be both first order and second order effects.
The first order effect is just price sensitivity. People will decide to take public transportation, drive, take a conventional cab (which now has an app)--or just skip going out for the evening--if prices, say, double.
The second order effect is that there will be fewer passengers which will lead to fewer drivers. This probably doesn't matter much in a big urban core. But in marginal areas, such as where I live, it may be the difference between a viable service and an unviable one.
I think that's very hard to predict. Just 5 minutes ago I had a conversation with my ex about how I always use Uber for ad hoc travel despite the fact it's often significantly more expensive than the local minicab companies, because they can get someone here much faster. Often it's a 3 minute wait, while I otherwise might wait 10+ minutes. Their app also gives me more reliable feedback.
If I schedule in advance, or need more flexibility in car type, then the minicab companies win, but it's very rare for me to pick them because of price, even though they're often much cheaper.
But of course not everyone can afford the luxury of paying extra, and will just factor in longer waits instead.
In a conversation where “real” can be partially defined as “are they worth their market cap”, saying a company has a high market cap does little to convince me. In fact it’s the opposite: it implies a long way to fall.
Market cap is just a representation of what the market thinks a company is worth as applied to a relatively small fraction of the stock.
Compare to a casino: people think that the ball will land on black and are willing to put their money down based on that. That doesn't mean they are right. In this case there is much more of a casino mentality at work that determines Ubers stockprice than that the underlying fundamentals are solid and sound enough to compute a price that is reasonable.