Niche Social Networks by Another Name

Lately I’ve seen several discussions about “niche social networks” and whether or not they can succeed.  The other day it hit me that they already exist.

Look at the user community that springs up around niche discussion forums.  For an example I’m familiar with I’ll take RailroadForums.com - a site devoted to railroads, railroading, railroad photography, and historical railroad preservation.  On the site folks sign up, participate in forums, post their photos, take part in polls, and generally socialize.

You can’t explicitly add someone as a “friend”… but so what?  Relationships naturally develop.  It’s still a social network.