In Brooklyn, Uber is now bigger than taxis

A more interesting comparison would be Uber to Gipsy/black cars. Those are going down in droves as the drivers move on to Uber and Lyft. Not a big impact for the drivers themselves, I suppose, but I've seen a lot of those little, "local" black car telephone stations closing down. No point in calling someone and waiting an indeterminate amount of time for a car when you can use an app and see where the guy is.

That impact is probably just much harder to measure though since everything, especially the payment, is a lot more informal.

Green taxis, a new category, are only permitted to pick up hails outside of lower Manhattan. They're useful for going between outer boroughs but are reluctant or unwilling to take you to lower Manhattan because they can't pick up a hail there.

There is also another, long-standing category known as "car service", where a central dispatcher reached by phone sends you a towncar/minivan/SUV either at a scheduled time (say, for an early flight or your regular work commute), or as soon as possible. Like Uber, they may have an "account" for you so you don't need to provide payment information to the driver, but nowadays many of them have Stripe too. Prices are arguably better for airport rides than cabs.

I live in Central Brooklyn and my impression is that there are far more Uber "U"s than any of the other categories, at least in my neighborhood.