#Facebook, #IRC or #Twitter. At best these are quite diverse examples of social networks. When you consider these examples, they have attributes that are functional to the extend that they are all widely used by Wikimedians.
When people then say that social networks have nothing to contribute to the daily practice of working on one of the Wikimedia projects they are absolutely wrong. They do not know the facts or their idea of what we do and how we do it is severely flawed.
Wikipedia is a crowd sourced encyclopaedia. All the time new websites and wikis pop up in order to provide visibility to a project; to crowd source something new. There is a website like WikiLovesMonuments.eu because the Wikimedia Foundation does not offer social network functionality. And yes, they reach out to Facebook and Twitter as well.
The arguments used against social network functionality for Wikimedia are missing the point. We are doing badly as a social entity because we do not support the groups who are active working together ourselves.