This is not very scientific. I got 4.8 which means absolutely nothing to me.
I've heard of people in my city having trouble and getting a driver to accept, most probably due to him having a low rating (whereas I never have trouble finding a driver)
Your request for service includes several non-price elements to it, one of which is your perceived likelihood to be a hassle (and reflected in your star rating), one is the amount of unpaid travel required to get to you, and one is what the driver perceives as likely to be your destination. All else being equal, drivers would prefer to end up in portions of the city with a high density of quality fares (say, an airport, the startup district(s) in SF, etc) as opposed to portions of the city with a low density of quality fares (say, the outer edge of the service area).
If drivers make a habit out of taking "bad" trips, their Uber business gets meaningfully less lucrative. Accordingly, expect them to actively avoid "bad" trips. If one's travel patterns routinely result in drivers perceiving you to require "bad" trips, one is going to have a far different experience with Uber relative to a high-frequency no-hassle business traveler.
If I knew why somebody rated me below 5 that would be a different story.
You don't tip with Uber - 'gratuity' is already included. Regardless, the rate-the-customer screen is seen immediately after stopping the trip
I suspect most drivers, like most passengers, give a 5.0 to almost everyone, but dock points for being a dick. It just seems there's no other way to differentiate passengers, since they'll be paying the fee regardless.