Actually, everything I've read says they are in mature cities. Leaked numbers say they're stupendously profitable in their oldest markets: nyc, sf, etc. They are losing money overall because they subsidize drivers when they move into new markets. But the key is always to look at existing markets.
The quickest numbers I could find were leaked in 2014.
est yearly rev run rate city
======================= ====
$212+mm sf
$312 mm nyc
$141 mm dc
$150 mm chicago
======= =======
$815 mm total
I guess the larger question is how do drivers respond when their rates get dropped after a market is mature. I imagine the answer is different depending on the market.
Those above cities are, I believe, post rate drops. Also other leaked numbers have said Uber continues to grow. My guess is driver happiness doesn't impact Uber's business much; our economy seems to generate enough desperate people that they have a nearly never ending stream of people willing to drive for $5/hour (a reasonable estimate of an UberX driver's true net comp.)
The quickest numbers I could find were leaked in 2014.
http://www.businessinsider.com/uber-revenue-rides-drivers-an...edits: made table