One of the drivers that I had in Europe has his own car service. Ever since he started with Uber, he said he is making more money with them then he was on his own. His business is now 80% UberBlack and 20% his own. He , now, only works privately with his old, regular customers.

He said that Uber expects drivers to make, at least, 45(?) trips/month. (don't quote me on the 45. I think that was the #.) if you drive 45+x trips, Uber gives the driver a bonus. If a driver goes 45+x+y trips/month, they get another bonus. The driver I had loves that system.