Judge and Be Judged
Some taxi drivers are chatty, and some are stoic. Same goes for riders. But there's never any mistaking the taxi driver for your friend. Driver in front, passenger in back, and sometimes a scratched-up window between the two.
Not so with Uber. It's like being picked up by a friend you never knew you had. You can sit in the front seat. If you've got luggage, it may go next to the driver's kids' toys in the trunk. You will almost certainly be called on to make a little small talk as a passenger.
At the end of the ride, driver and passenger both will be prompted by the Uber app to rate each other. The idea is to crowd-source out the crazies, so try to put up your least psychopathic public persona while in the passenger seat.