I think this drop is due to the recent huge selling done with bitcoins. Holidays have just past, and that was the time when people might have thought to encash or spend their bitcoin holdings. And when there is a greater number of sellings of bitcoin i.e. more availability of bitcoin in the market, its value decreases. Also the prices went really high which made speculative sellers sell off their holdings.
Also, because the sellings were made by individuals and not some giant company, the fall in price is not very huge but marginal. Its kind of stable at a certain point.
With start of new year, hopefully new users will join bitcoins, may be investers may come in, and old holders shall try to regain their hold which will again create a virtual scarcity of bitcoins in the market and in result the prices will spike up. Sooner or later, the prices are again going to grow and probably stabalise for a good while.