A lot is being said about the 45 minute threshold for unlimited annual members -- cross the threshold and you start paying fees. This means that if you take a single ride for greater than 45 minutes without docking and switching bikes, you will have to pay more than the $103/year.
I think this is a non-issue, and Google Maps is around to back me up. If you use the bike directions on Google Maps, it will tell you the estimated time of your trip. So I tried it out. I started at West 60th Street & Columbus Avenue, at the northern edge of CitiBike's initial station range. Then I plugged in Battery Park as my destination, at the southern tip of Manhattan.
According to Google Maps, the route along the Hudson River Greenway should take an average rider 33 minutes, leaving 12 minutes under the 45 minute threshold in case of delays.
CitiBike offers protection from crossing the threshold. Just dock the bike, wait a few minutes, and take out another one.
CitiBike is primarily for transportation, not bike tourism or long-haul rides. You can do these latter functions on CitiBike, but you will need to switch bikes at an interim station. You're better off renting from a bike tour outfit or a local bike shop, which have better bikes for cruising anyway.
As for the $103 annual fee, it is an amazing bargain! And the more you use CitiBike, the cheaper it gets!