I doubt that difficulty is going to drop, at least not for a very long time. We're currently seeing the beginning of the end of the mining-manufacturer bubble; the companies sit on thousands of chips that they can't sell anymore. I expect a big wave of dying ASIC companies, but till then, the only choice of these companies is to turn to self-mining with their own unsold equipment. ASICminer is an example of that, but I think that the recent rise of DiscusFish's percentage in global mining is all the cheap ASIC manufacturers in China starting to self mine or cooperate with big industrial mines in order to get rid of their pre-produced equipment.
If the difficulty increase like this, soon some giant miner would hit break-even for their electricity...
