Not only that, but there's $570000 in leveraged long positions on bitfinex according to https://www.bitfinex.com/pages/stats , which is about the same as the order book at Bitstamp!

If my math is right, a long position taken at $105 at 2.5:1 leverage and 90% reserve would get liquidated at $75.  Since there's only 3100 btc to $75, someone could sell 3100 btc down to $75, then likely catch the subsequent liquidations to regain their bitcoin holdings at a lower price.  Hmm.  Perhaps that's what the eager bitstamp seller was trying to do when they dropped the price to $90?  Or perhaps there was an eager seller to $95, and the rest was the liquidation of a bitfinex user that took a long position at $120+?  Big liquidations like that used to happen all the time when Bitcoinica allowed 10:1 leverage.