Social Media can be mined for three pieces of information: Content, Marketing Metrics, and Network Relationships. For example, Twitter provides rich text content that can be mined and analyzed. Facebook, on the other hand, provides great metrics to see how well an organization is drawing attention to its posts. Finally, just about any social media platform contains relationships between people and the content they post.
Here are some examples:
Many social media sites have APIs (application programming interface) that provide access to their content, including Twitter, Facebook, and YouTube.