I am certain most people placing hardware orders are underestimating the difficulty increases. The calculators like
http://mining.thegenesisblock.com only work from past data, they have no idea about the impact of new ASIC vendors releasing hardware onto the net until it has happened. eg. Nowhere in their forecast is KNCminier included, the predictions are based on the vendors that have shipped already! BFL have been rolling out 50-60GH/s Singles at quite a pace lately, and have a lot more to go. BFL bulk chip sale shipments are due soon, so BFL will probably account for over 600TH/s of the net hash within the next month or two, and could be closer to 1PH/s if they ordered a 3rd wafer batch. Add to that PH/s from KNCminer, and whatever Cointerra, Hashfast actually do, and you will see how wrong the mining calculators are.
My bet is that it wont be worth buying hardware that is more than 1watt per GH/s as the energy cost of mining a coin is going to rise much faster than most people have predicted. Of course people with less efficient hardware will keep mining even if they don't cover the electricity costs, and that will compound the problem. You may be able to under clock your rigs down to 1watt per GH/s.
