http://readwrite.com/2013/10/08/bitcoin-probably-gets-its-value-from-illicit-use#awesm=~olJf93Y1j5jz40Bitcoin's drop following the Silk Road shutdown suggests that illicit activity exerts a non-negligible influence on Bitcoin value.
The anonymous crypto-currency’s value dropped suddenly last Wednesday after federal law enforcement agencies shuttered Silk Road, an online black market used to buy and sell illegal drugs with Bitcoins. According to Mt. Gox, one of the most popular Bitcoin exchange services, the value of the virtual currency plunged from $140 to $129 the day Silk Road closed down. Trading volume in Bitcoin simultaneously skyrocketed.