I had issues with the app's GPS in the loop in Chicago. I would text the driver to confirm my exact location and to tell them I was wearing a red jacket and that made things easier.
Someone mentioned sharing a ride and that will only happen if you select an uber share ride. There are options - a regular car, a larger vehicle, a shared ride, etc. I've often been picked up in a larger vehicle when I didn't request it and still paid the price for a normal vehicle.
I've had two issues ever - 1 with a jerky driver in Brooklyn who insisted that I set my pin across the street from where I actually was. Even if true, he just had to turn around to get me. The other, the guy accepted my ride and the app said he was 5 min away. It showed that he was finishing a ride a few blocks away, but he didn't arrive for almost 20 min. He got lost on my ride, so I'm guessing there was a bit of that leading to the delay.