An NYU study of CitiBike supports the idea that the system is most useful for short trips that fall between “too long to walk” and “too long to take transit.” It also confirms that the bikeshare system is being used as a transit connector:
The most popular Citi Bike station in the city is at Pershing Square North, near Grand Central Terminal — where 16,556 trips began last September. There are nine bike sites within a quarter-mile of Penn Station, eight within a quarter-mile of Grand Central, and 10 within a quarter-mile of the Port Authority Bus Terminal.
The vast majority of Citi Bike trips, 98%, are shorter than 45 minutes, and nearly half clock in at less than 10 minutes.