1 months .4 46% loss
2 .62 71% loss
3 .75 86% loss
4 .82 94% loss
I think this last bit is the most interesting/useful for would-be miners to understand. It is the reason people become absolutely livid with delays from BFL, Avalon and any other ASIC seller as delays rapidly destroy any potential for profit (other than profit for the mining equipment companies of course).
I imagine in the future that more savvy miners (unlike the current math-challenged crop) will demand a purchase contract with built-in discounts off the agreed purchase price to offset any delay (46% discount for 1 month delayed, 71% discount for 2 months delayed etc...).
I, for one, will never "pre-order" mining equipment without such a contract in place or without the funds being 100% in escrow to make a total refund possible if/when a shipping date slips.