A key to running successful "social networking sites" is to remember that they're just communities. All communities, online or off, have one thing in common: members want to belong, to feel like part of something larger than themselves. Communicating effectively, setting clear and specific expectations, mentoring contributors, playing with trends, offering rewards, and praising liberally (but not excessively) can harness your members' innate desires, and nurture great content in the process.
Asymmetry, asperity, simplicity, modesty, intimacy, and the suggestion of a natural process: these attributes of elegant design may seem relevant only to a project's aesthetics. But the most successful web designs reflect these considerations at every stage, from idea to finished product. Bring heart to the experiences you create by infusing them with intelligence that transcends aesthetics and reflects the imperfection of the natural world.