See the construction plans for a high-speed train from staten island to manhattan (nyc). It should make going from SI -> Manhattan take about 20-30 mintues saving an average commuter about 20-40 minutes per ride. Gets a ton of cars off the road, thus making the other commutes faster, less cost, etc. Commuting in NYC is quite problematic.
it does not matter. well, i don't know NYC. let me talk about west coast. SF is fine for buses/subway. But if i live in SF, and need to go to LA, even if bart install the fastest train there is, it's of no use to me, as i can't even get a taxi in a decent manner in LA. i will have to take my car, or rent one there. or at least commute with some friend.