Social Design Best Practices - OpenSocial - Google Code

Article has 9 good best practice principles for developing social applications:

If you're new to developing social applications, it can be difficult to immediately grasp how good
applications facilitate fun and meaningful social experiences. To accelerate your learning, we've come up with a list of a few light-hearted recommendations around building good social applications. Not all of these "best practices" are necessary in every case, but they might spark thoughts about finding new users, keeping old ones, and leveraging the social graph for fresh content and viral spread.....

Social Design Best Practices - OpenSocial - Google Code