Well over 600,000 developers participate in a topcoder community that not only allows them to expand their development skills, but also gives them access to projects where they can get paid for participating.
It's no secret that Facebook's Graph API and widgets have contributed a great to Facebook's success and never-ending permeation of the web as we know it. Looking to make a similar move, LinkedIn has recently expanded its own developer platform and LinkedIn API. The new LinkedIn tools aren't just aimed at developers. With just a couple lines of code, you can begin integrating LinkedIn in to your web page with a variety of plugins and widgets.