Here's the deal with mixing services. Yes, Bitcoin Fog uses independent wallets and addresses with zero taint between them. But they have to keep a separate database of accounting details to link the two. You transfer 10 BTC into your account and expect to get 10 BTC back (minus the fee). That transition between addresses is not stored in the block chain, which is good, but it is stored in some separate database under Bitcoin Fog's control. You're essentially putting your trust in Bitcoin Fog that they aren't LE, they are not working for LE, and they delete those database entries after the transactions are done. Maybe they do, but we can't be sure. Blockchain.info also has an anonymization service and they claim to delete the database entries after 6 confirmations. Again, maybe they do, but we can't be sure. The safest option is to transfer through multiple mixing services. The chances that all of them are operated by LE, or are working for LE, or that they save their logs, are much lower that way. That's for the uber-paranoid. Keep in mind that no SR buyer has been busted through an analysis of bitcoin transactions, and a lot of people are doing direct transfers. Realistically, this is a minor threat, for now.