Looks like somebody messing with MtGox again to me.
Went down to $190, and now (maybe) heading back up again.
it backed down to almost $150 now. What's happening looks like 1 of 2 things (or both combined):
1) the bubble has burst. The climb from $20 to $280 was an obvious bubble, but no-one knew its ceiling (my guess was gonna be around $350). The drop in price has multiplied perceptions that the ceiling was hit, and we will see very rapid rippling of this across the network. and will test a lower valuation limit today or tommorrow. (probably around $100) and bounce up to hunt for a new happy medium around $125-$200 range
2) BEAR RUSH. This is more common then many might think, and boils down to a few heavy hands that hold thousands of coins putting a significant portion for sale below market. this drives down the asking price, saturates the market, and triggers others to panic sell. The heavy hands then re-buy for cheaper and walk away smiling. Right now we would be in the tail-end of this mechanism, and should see some large asks in the 125-175 range as these people rebuild thier wallet with almost 2X the coins they had prior.
I think both have occurred, and its hard to judge where the price will level out. I think >$100 is entirely justified for bitcoin at this point, and we could easily resume the rally at a more linear pace to test $300 again this week.