I think that such a program is doomed for failure in the United States unless you properly secure the bicycles. We just have too many people in our culture that think it is OK to take or vandalize, someone else's property.

Here in Pittsburgh, they have a sharing program. I don't know a whole lot of details on the project but the bikes are stored in bike sheds. The lock can be opened with a swipe card. I would assume you need to provide a credit card to get a swipe card and would be responsible for the bike if it is lost or stolen.