Here's some info from Portland's bike share site. I've also included helpful links below:

WHAT HAVE WE LEARNED FROM OTHER CITIES

People bike more after joining bike share, even if they own a bike.
Bike sharing makes getting around more convenient for everyone. Two thirds of Minneapolis bike share members reported biking more after joining even though 77% owned a personal bike.

Big systems work, small systems don’t.
There are hundreds of places in Portland that people want to go to. The more stations you have, the more likely it is that a bike sharing station is near your destination. Too few stations and the system isn’t a practical choice. DC’s first system had only 10 stations and very little use. DC metro's new system has 140 stations and had 1 million trips in its first year.

Bike sharing works best in dense places.
Bike share is designed for short trips under three miles and 30 minutes. Cities get the most bang for the buck by locating stations at popular origins and destinations, such as workplaces, schools, and shopping districts. As the system grows, additional areas can be added.

Bike share stations need to be close together.
Whether you’re parking your car or bike or getting off transit, you want to be close to your final destination. If your bike share station is full, nearby stations provide a convenient back-up option to return a bike.

Theft and vandalism aren't major concerns.
Before bike sharing came to the North America, a lot of people worried that the bikes would end up vandalized, stolen or at the bottom of the river. That hasn’t happened.

Today’s bike sharing systems are built to withstand urban conditions – including people with ill intentions. Users must use a credit or debit cards to check out a bike, which creates user accountability. Minneapolis had one bike stolen in 2011. DC/Arlington’s Capital Bike Share theft rate is less than 1%.