I've been watching Cryptsy and Mintpal very closely this last couple of weeks and I've noticed that the price drops seem to be orchestrated by huge sell orders (several or tens of BTC worth of DRK) which have no prospect of being filled. In fact the volume of sales is pretty modest in comparison with the size of the orders... which don't seem to reduce at all.
So who's in control of all this Darkcoin? And why do they feel that it's in their interests to devalue their own investments?
Could they be looking for more cheap coin to fund Masternodes?
The problem comes when they undermine confidence so much that nobody else wants to invest. It may eventually offer a valuable service, but that service is by no means unique; and if the big players are continually manipulating the market for their own gain, then the casual user will be looking elsewhere.