I have cancelled an Uber car a couple of times – in Moscow, and I did not charged for this. Only because the cars were unable to find me, and the drivers (understandably) did not want to call my UK number.
Having used Uber all over the world, NY, LA, London, Wakefield(!), Melbourne, Sydney, Rome, Rotterdam, I now find the service an indispensable part of my working life. Even Surge Pricing, which I hear complained about a lot, means more drivers come onto the streets, increasing availability.