This is a major problem I've had with Uber in Mumbai and rather strangely not anywhere else. I'd say about 50% of rides wind up with at least 1 driver cancelling. Often the same driver picks up the fare multiple times and then cancels a few minutes afterwards. Highly annoying.

My parents use Uber regularly and do not have the same issues - but then again they tend to request pickups in more respectable parts of town than I do. They do not use UberX or the new UberGo though - the wait times for these relative to UberBlack are often ridiculous (and UberX is almost always on surge pricing in Bandra).