Online social networking has become one of the most popular services on the Web. However, current social networks are like walled gardens in which users do not have full control over their data, are bound to specific usage terms of the social network operator and suffer from a lock-in effect due to the lack of interoperability and standards compliance between social networks. In this paper we propose an architecture for an open, distributed social network, which is built solely on Semantic Web standards and emerging best practices. Our architecture combines vocabularies and protocols such as WebID, FOAF, Semantic Pingback and PubSubHubbub into a coherent distributed semantic social network, which is capable to provide all crucial functionalities known from centralized social networks. We present our reference implementation, which utilizes the OntoWiki application framework and take this framework as the basis for an extensive evaluation. Our results show that a distributed social network is feasible, while it also avoids the limitations of centralized solutions.