While everyone is busy talking about Charlie Shrem's arrest, no one seems to notice the REAL reason for the market plunge. That is, 3 hours ago Bitcoin was officially banned in Russia. No English language news source yet, but Russian newssites are all abuzz about it: http://bitnovosti.com/2014/01/27/bank-rossii-ozvuchil-poziciyu/
Use Google translate, everything is quite clear. Everything is banned, including mining, exchanges, transfers and payment processing. Each company accepting Bitcoin will be automatically charged with "supporting terrorism".
Russia wins the dubious distinction of the first country in the world to officially ban Bitcoin (unlike earlier Thailand myth).