Some large holders - one in particular over the past 2 weeks it would seem judging from the mastercoin-explorer - are selling at a faster rate than the incoming bids and are driving the market lower. The volume on the exchange cannot support the large quantities they are trying to sell so quickly. The entire bid volume is just 39 BTC at the moment. Either the sellers are going to have to adjust their expectations on how fast they can sell or the price will keep dropping. I suppose this is good news for people that want to invest in MSC.