strictly speaking on power being the only variable I wouldn't even suggest to "mine-for-profit" basis with power rates higher than $0.10 ( and you are unable to get write offs or reductions. )

The real factor in the transition period of ASIC units will ultimately be delivery time, when difficulty is lower and the ROI is much higher.

Let's take this conservative example. using http://bitcoinx.com/profit/index.php

6 times the current difficulty
$.25 power cost.
400W
60GH/s

your break even time is 81 days, thats little over 2 month, of course assuming you can only maintain this ROI rate for 12 days or so, you would have effectively made 15% of your invest back.

with the current trend of everybody pushing their shipping date back I feel everybody has over estimated how quickly the difficulty will rise.

Let's assume Tom sold 1000 units, that's give or take 50TH/s,
Avalon only selling 300 units first batch, ~20TH.
BFL sells a crazy estimate of 2000 units, 120TH.

that barely adds up to 200THash, which is about 10 times the current network rate, and if difficulty goes up by a factor of ten using the same formula above. your ROI is 156 days.

honestly, it isn't that bad.

disclaimer: Avalon nor Yifu will be responsible for information provided here based an educated guess of future Bitcoin mining difficulty.