This is a v.interesting blog article about the highs and lows of social networking sites.
Basically it points about that what goes up often comes down (with a plateau inbetween), and this is especially true of community-driven sites.
The key thing to consider about social sites is the “social” bit of them. They’re essentially like bars on the high-street, and we’ve all seen the latest trendiest bar come and go and often make money riding the trend.
Check out the blog post here