Recently there have been some signs of aging in the larger social networks, or at least reports of reaching middle age. These include the inevitable decrease in value that comes with an increase in noise, and a predicted drop off in users. While both of these are likely true they are also probably exaggerated because they make good headlines.
Yes, the headlines are predicting the demise of Facebook are good, but more importantly when stories like these appear they begin a conversation about network effects and the evolution of social networks.
The first thing to remember is that different networks operate differently. Limiting this post to just two of the most common (and most conversational) social networks Facebook and Twitter encompasses the most common types of relationships.
How the networks operate:
Facebook: Symmetric following (users must follow each other) and information is spread in an algorithmically curated stream.
Twitter: Asymmetric following (users can follow whomever without being followed back) and information is spread in a users stream in a constant flow curated only by limiting who the individual user follows.