In about 6 hours the difficulty will be about 9,000,000
At that difficulty, 10GH/s will make about 0.55 BTC a day.
Use that in your calculations for the next 12 days
... then of course multiply 0.55 by approx 0.84 for the 12 days after that ... and continue doing that until BFL release their hardware
That's a reasonably good estimate ... with the totally unknown number in there "until BFL release"
(coz when that happens the difficulty will sky rocket)