There was a comment on the Silk Road forums (in the context of replying to someone wondering whether buying from a seller with 0 reviews was very risky or not) to the effect that the Gawker article had caused SR to jump from a few hundred accounts to over 9000.

A decent number, granted, but likely most of them have not engaged in any transactions and never will. On the other hand, another poster mentioned that there is another Bitcoin+Tor market site by the name of BlackMarket (or something), so SR is only part of the picture.