Remember when wikileaks couldn't get donations because "pressure" was put on paypal, mastercard & visa not to process those payments? Bitcoin.
Wanna donate to the piratebay? Anonymous? ...bitcoin.
Megacorps wanna donate to a political campaign without being found out later on? ....bitcoin.
There's risk in the movement of a day's cash flow by BTC, but probably not much higher than the risk of transferring cash in your personal car.
If governments were really devious they would replace their cash with a non-anonymous cryptocurrency like BitCoins. That would make it hate for the underground economy to avoid the police or taxation.
It's true that without using a mixer (aka "money launderer") Big Government could seize the service to get your name... but what about https://localbitcoins.com/ ?
Asking their customers to do it for them is unrealistic. Their target audience is not "HN techies", but rather "general population". Maybe in the future having the customers do it will be a realistic solution, but maybe in the future it will be fully legalized anyway...