since a couple of months there is the possibility to rent a bike for 10$ / 24h (but max ride is 30min). it is called citibike and you have it all over downtown and midtown and parts of Brooklyn.
to ride a bike in NYC is very interesting. in lower Manhattan you often have separated space for bikes. but often they are blocked by cars or cabs. also it can get difficult to find the right route because there are only one way streets. might be helpful to have Internet access on your smartphone.
new yorkers wear helmets, and just like pedestrians they don't mind traffic lights. many use front and rear light on their bikes which I would definitely recommend.
greetings to everyone from central park!