I have written a lot aboutbike-sharing, and I work at a company now that designs and studies these systems every day. I especially love when it'sintegrated into a larger multi-modal system(trains, buses, etc). But if you had been there when bike-sharing was born (probably in many places in parallel at different times...), you might not have believed that it would ever work, at least not at the scale that can be found in some cities (Hangzhou in China has about 65,000 bicycles, and Wuhan about 90,000!). That's because, while bikes are relatively low-tech, managing the memberships and stations without getting all your bikes stolen is a pretty high-tech endeavor, and we're still figuring out the best way to do things (no two bike-shares are exactly alike).
It took many iterations before bike-sharing became truly viable:
Bicycle-sharing has come a long way since the 1960s, when 50 white “free bikes” were scattered around Amsterdam, only to be promptly stolen. A second generation of coin-operated bicycles still got nicked. A third generation solved that problem with electronic docking stations and credit-card payments. (source)
And now a fourth-generation is emerging with technologies like mobile solar-powered docking stations, smart software handling the distribution of bikes, more mobiles apps, etc.
Growth in bike-sharing is strong, even in more difficult markets like the U.S.:
According to a study by the Earth Policy Institute (EPI) in Washington, Europe accounts for most of the programs, but Asia has the largest number of shared bicycles, with over 350,000 in China alone. Even in often bike-hostile America, which in 2012 had 21 schemes with 8,500 bicycles, the EPI expects the fleet to more than quadruple by 2014, to 37,000. In London, which has 8,000 shared bikes, another 2,000 will be added later this year. In Paris the Vélib scheme, which opened in 2007, has already racked up 173m journeys. (source)
So if there's a bike-sharing program in your city but you haven't tried it yet, I encourage you to! Go for a ride with family and friends!
If you're curious about bike-sharing around the world, there's a pretty complete list here with number of stations and bikes.