This is actually a classic case of how traders are using Mt. Gox to manipulate prices. Notice how the price of bitcoin has plunged nearly $30 while this has been going on.

When they get the price down far enough, they'll buy back massive amounts and repeat the process for as long as Mt. Gox allows their API to process massive amount of micro transactions from a single seller.

This process gives them a guaranteed way to buy low and sell high over and over again.

Here's a more detailed explanation from http://www.computerworld.com/s/article/9238571/Largest_bitcoin_exchange_Mt._Gox_39_throttles_39_trading_to_tame_price_swings:

Miscreants are also trying to manipulate the virtual currency's price by using Mt. Gox's API (application programming interface) to submit trades for very small fractions of bitcoins. It is possible to watch real-time trades on Mt. Gox through services such as Clark Moody's website, which shows Mt. Gox's order book, or the prices at which people want to either sell or buy bitcoins.

During heated trading, it is possible to see a rapid influx of very small quantities of bitcoin on both the buy and the sell side. A sell order for .0111 of a bitcoin, for example, would represent US$1.33 if one bitcoin is trading for $120.

It doesn't appear that buying or selling a $1.33 slice of a bitcoin would be very practical given the small economy so far for bitcoin services, although the market is growing. But entering lots of small sell orders, for example, can give the impression that bitcoin's price is falling even if it doesn't represent the broader market sentiment. Traders can submit more than one transaction using Mt. Gox's API.