In London, the night bus route I tend to use (to Walthamstow from central London) runs at a slightly lower frequency overnight - just once every ten minutes. It's about as fast as the tube because of the more limited traffic.

And you use the same old Oyster card as during the day. I assume it's just as cheap - 80p or a pound per ride? Cheap enough that I don't even keep track.

I agree with the GP - the overnight services outside of limited routes in NYC aren't flash, and most of the rest of the US metro areas are appalling.