Yet it seems like Silk Road would be an improvement on Craigslist's adult services, which was apparently popular. AFAIK Silk Road sites offer profiles and ratings for customers and sellers.
Pragmatically, sex workers are already subject to people constantly trying to rip them off, and bitcoin usage/intense anonymity of clients is a step in the wrong direction, from their perspective. A rating system for customers and workers would be fantastic, but you'd be really hard pressed to get a client to sign up for anything attached to their name, and there are already venues for workers to advertise and some are able to network and get feedback about potential clients. There have been alternatives to CL for a long time, but CL was used mostly be clients who didn't want to communicate with anyone except for the worker and potentially have any information about them recorded. And of course, seeing as how the Silk Road drama played out, perhaps it's not the best model to emulate.