I am currently GPU pool mining at a total of ~1500MH. This produces slightly less than 0.1BTC/24h at present difficulty. With all those ASICs going on, difficulty will likely skyrocket, so the big question is, what the difficulty will be in a month?
That's the question, and why I figured 20BTC would be safe. It seems it should take somewhere between 45-65 days to break even at 20.