Looking at the different variety of social media sites, I feel they fall into these categories: SNS, Niche-based Communities, and Content Sharing.
Social Network(ing) Sites
Any site that was built for communication with friends or strangers, socially or even professionally. This includes sites like Facebook, Twitter, LinkedIn, etc.
Communities based on specific interests can vary greatly from sites for teachers to pet-lovers. Some examples include Catster, Steam, and BakeSpace.
I would consider these to be SNS, however I would not consider all SNS to be for a specific niche or interest. Facebook, for example, was created with the sole intention of connecting people. Mark Zuckerberg, the creator of Facebook, even stated, “When I made Facebook […] my goal was to help people understand what was going on in their world a little better” (Zuckerberg 2006). It’s about sharing information and controlling who sees it. When it comes to special interest groups, the information that is shared is usually centered on a specific topic or caters to a certain group of people.
When sharing news, bookmarks, files, videos, or even personal writings (blogs), I believe sites like Reddit, StubleUpon, and Flickr fall into this category. These sites are focused in the type of media that is shared.
As I said in my post Web2.0: social media is about giving people the power to share, communicate, and collaborate. While all of these are means in which people do those things, I guess what really differentiates them is what they are geared toward when communicating. I find SNS to be communication-based regardless of the type of information, Niche-based Communities are interest-based, and Content Sharing Sites are content-based.
Zuckerberg, Mark. (2006). An Open Letter from Mark Zuckerberg. Retrieved from: http://blog.facebook.com/blog.php?post=2208562130.