I've used Uber a handful of times.
Once, trying to get an Uber from Edgware Road late at night, the driver "cancelled" my journey costing me money even though he didn't even turn up. I didn't realise till a few weeks later.
Another time, the charge for the fare was far more than Uber told me it would be as it only gives you an approximate fare
Once, I got an Uber from Belsize Park to south of the river, it was probably the best taxi I have been in for a long time, a Seat Alhambra with a glass roof etc, spacious, friendly driver etc. It also saved me the hassle of looking for a local minicab office.
I usually use the local minicab office as I have the number saved in my phone and I know the fare will be consistent, every time I have been in an Uber the driver has complained that they aren't making much money with Uber.