Post-2001 and the Patriot Act, bank tellers, stock brokers and insurance agents have all become lay intelligence officers under "Know your customer" compliance requirements. Informal value transfer systems, barter/black-market, are only a problem in terms of taxation.
Mt. Gox and money exchanges were functionally brought under these KYC compliance regulations and it is only a question of time until bitcoin users will have to speak about the source of the money. Sources are important because that's how taxes are levied.
If you can show you have paid taxes on your money, it's rare to have a problem.
We have systemic trillion dollar annual deficits, so tax collection efforts are being ramped up. It's why you get 10,000 IRS officers hired instead of 10,000 doctors for a national health care system reorganization.