What's old is.. still old. Except the difficulty is not 3M any more, it's about 27 Billion now.
Necro-bump. Due to the scheduled halfing of the block reward every four years, the new number is:
Average BTC per Day = (megahashes per second / difficulty) * 502.91419New realistic examples using today's network statsRadeon HD 5830:
300 Mhash/s at 3438908.96 difficulty =
( 300 / 3,439,000 ) * 502.91419 = 0.043 BTC per day
or 1.32 BTC/month ≅ $16/month
BFL Single FPGA Miner:
832 Mhash/s at 3438908.96 difficulty =
( 832 / 3,439,000 ) * 502.91419 = 0.12 BTC per day
or 3.65 BTC/month ≅ $45/month