The paper trail would be in the distribution. Virtual money would be even more obviously trackable than paper money. Its pie in the sky, if it were feasible all the hackers would be doing donuts in Lamborghini's after sitting courtside at Miami Heat games
Again, NSA, drones, billions of surveillence cameras, GPS tracking/monitoring ...err "location" on mobile phones.. If you ask me the government loves the new digital world more than any other, they're doing a better job of fucking people than the fucking Romans or the damned Crusaders