First it was MySpace. They dominated for years and eventually became isolated from assorted social environments that are more prevalent now. Not to mention, everyone who harnessed MySpace remembers having Tom as a friend.
Eventually the trend arguably withered and gave way to new applications such as Twitter, LinkedIn, Foursquare and Facebook, just to name a few.
These environments have seemingly remained relevant, despite the monopoly of social media sites that have recently gained traction.