I tip my Uber drivers a few bucks each ride. It's still cheaper than a taxi and the service is much better. The drivers rate us too and low rated passengers are less likely to get picked up.
I found an Uber driver in my neighborhood. Because I tip him well, he gave me his phone number so I can schedule a ride with him. For example if I need a ride to the airport at 4 in the morning when there aren't any other Uber drivers online.