Based on how the ASIC miners are coming online by the thousands, and the fact that difficulty have been increasing at a steady rate of 1.26% since beginning of year, there's no reason to think that the rate of difficulty increase will ease soon over the next few months.

Meaning if you buy a ASIC miner that have no other use than mining BTCs:
70% of profit is mined in the first 3 months!!!!
97% of BTC is mined in the first 9 months!!!!!!!!!!

The economics of buying ASIC miners from Butterfly Labs makes no sense.  Considering that:
- They are extremely slow in shipping, 2 months or more meaning a year or 10.  They are still trying to ship the June 23rd order from LAST YEAR
- No refunds, all payment upfront.

While they are busy using the rigs to "burn in testing", they are getting a lot of BTCs for themselves for sure while their customers are waiting for them to ship.  So if they delay the order by 6 months or so, they would have earned 90% of the profit themselves.  By the time their customers receive their last gen order, it'll be obsolete because their little 5GH/s unit cannot compete with new 500 GH/s or 1TH/s ASICs.

Furthermore there's no data on power consumption, meaning that the power consumption is likely very significant.

So stay away from ButterflyLabs and don't be the fish biting their hook!