Darkcoin use CoinJoin method, much like Shared Coin service of Blockchain.info. We can still practice CoinJoin within Bitcoin system, therefore Darkcoin offer nothing new. CoinJoin doesn't hide your transactions completely, it just make harder to trace your money flow. With proper data mining and data analysis, your transactions might still be traced. And federal agencies have more than enough human & technology resource to do that. Zerocoin is another story, i'm excited to see what Zerocash will bring to crypto world.