Same in Bangkok. Taxis are plentiful and cheap. But like elsewhere if you flag one down they often refuse you if you want to go somewhere inconvenient for them. That's where a taxi hailing app like GrabTaxi is useful. It works like Uber except it's a taxi that picks you up. Uber exists here but hasn't got much traction (as far as I know).

NYC is actually one of Uber's most important cities. Don't forget that NYC is more than just Manhattan below 125th street. Getting a taxi in the outer boroughs was miserable. The green ones help but were a little too late. The black car services are entirely unpredictable and unreliable, doubly so if you are not of the ethnicity of the dispatcher/drivers they employ.

And let's not even talk about the number of times a cab driver straight up refused to take me to Brooklyn, both during the day and late at night. Totally illegal, but it happens all the time.

Agreed, when I was living in the Valley in 2003/4 public transportation was terrible and taxis nowhere to be found. But then I was driving a shitty Ford ....

Except when it's 4 pm and you want to go to the airport from Manhattan, at which point none of the million cabs are interested in picking you up.

Same with Hong Kong, Uber have started up there but I think they will struggle.

It also depends on where you are and the time of day. Even without rain it's not always easy to hail a taxi in Shanghai.