I find this interesting because when I was a kid, the only times you were expected to tip were a waiter, a bus boy, a valet, and your taxi driver. Now-a-days, we're supposed to tip for haircuts, coffee, carry-out, maid services, delivery people, trash collectors, frick' anybody you might make eye contact with when you're paying for something, they're supposed to get another 15%. I generally do, but it's expensive and exhausting.
I don't Uber, I sometimes use Lyft. I've always tipped thus far, even when the ride was really bad. I was really torn over it. Seriously, he was running stop signs, darting in and out of traffic, and speeding like 20 over. It was pretty terrifying. But there's that pressure.