Zerocoin? https://en.bitcoin.it/wiki/Zerocoin
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From the BitcoinMagazine article: "Some of the proposals which have been suggested in the past include: adding the capability to reverse transactions, confiscation of balances, creating a central authority that can whitelist and/or blacklist addresses, and requiring all users to register their wallets with a government agency. So far none of these have been implemented into the protocol but the pressure to do so is will only continue to increase, especially by venture-funded companies, especially in the USA."

If those things will happen to Bitcoin, I will leave it.