This isn't a complete, up-to-date answer, but Nicolas Christin estimated in August 2012 that 1.2 million USD worth of transactions are made every month. http://

This isn't a complete, up-to-date answer, but Nicolas Christin estimated in August 2012 that 1.2 million USD worth of transactions are made every month. http://arxiv.org/pdf/1207.7139v2.pdf http://arxiv.org/pdf/1207.7139v2.pdf I imagine that number has grown, but odds are that the vast majority of Bitcoin usage still isn't on the Silk Road. Also, buyers on the Silk Road have to be careful about which services they use to buy Bitcoin. If CoinBase isn't anonymous (and I'd guess it's not, since it uses bank transfers), Silk Road transactions could be tracked back to the purchaser's bank account.