Any BTC<->cash exchange would either be illicit or have very clear, robust records as required by the country that issues the cash currency. Here's an exercise

Any BTC<->cash exchange would either be illicit or have very clear, robust records as required by the country that issues the cash currency. Here's an exercise for you: prove that Joe purchased $100 worth of Bitcoins to obtain drugs illegally. You only know that they were purchased using a cash deposit to a BitInstant account, which was moved to MtGox. Neither of those accounts have IP addresses, e-mails, or any other type of personally identifying information. The bank doesn't have surveillance records anymore.