Yes. The big factor not addressed in most of the profitability calculators is the difference between mining now and 3 months from now. An eruptor blade (at 10 Ghs) that will pay for itself in about 2 months right now will return just a few dollars a week starting in March. Also, The huge volume of new terahash coming online in the next few months is most likely to skew the difficulty big time.

Morris