Toast: I know that's a double standard, but Darkcoin provides more than enough reason for the government to treat it differently than cash. The government benefits from the flow of dollars, while they don't have a piece of the cryptos (as far as we know, though some people think Satoshi was NSA). Look what the regulators are doing now with cryptos: they're drawing a line in the sand with the traceability ("anti-money laundering") and tightening up the banks. They'll force the real criminals to use cash or go with underground cryptos. Then watch them effectively shut down the underground ones by going after visible users, just like they did with some of the visibly illicit Bitcoin users (Silk Road, etc.). Yes, they have a double standard; it's partly to protect the dollar and partly because they don't understand this new world. Plus, their pride won't let anyone get away with blatantly ignoring everything they've been telling us. The government stays on that trail every single time, taking years if they must, and they do not forget.
That's why I said that when the federal agencies involve themselves, it's not "innocent until proven guilty." In a court of law, that is the standard, but they'll ruin someone long before that day in court ever arrives. Darkcoin has expressly gone against everything the government has been telling us we need as a minimum threshold in this field. I know it's supposed to be anonymous, but people will make mistakes and there will be some fairly obvious circumstantial transactions (e.g., a bank transfer and then a purchase of something for the same amount). The government will watch for awhile, learn, and if the currency gains any real traction, they will take some high profile actions that scare off a lot of people. Don't forget that when they finally got Al Capone, it was on tax evasion.
So I don't think this coin has a long future. But then again, Napster didn't need a future to be successful. It just needed a past and present before it burned out.