Couple of things that bother me
I must admit, as a taxi user, Uber does worry me for a couple of reasons.
1) Surge Pricing. Don't get me wrong, I'm well aware that cab companies will make you pay more at christmas/new year/etc. But all of those changes are well advertised, I know they're coming and when, and can plan accordingly. Uber, as far as I understand it, I won't know whether someone's chosen to up the price until the journey is calculated at the time. Kind of buggers up planning a tad.
2) Insurance, safety etc. Proper insurance and safety stuff is part and parcel of getting the private hire plates/taxi plates. Is the safety training and insurance part of the whole Uber deal, or can any tom dick or asshole with a car and a phone sign up?
Otherwise, booing a taxi through an app and knowing what it'll cost before it starts is a great improvement.