This is very approximate, but I thought you'd be interested in knowing that at the moment your hash rate is roughly equivalent to the amount of money you'd be making with the current difficulty and exchange rate.

For example, if you have 600Mhashes/s, your revenue would be roughly $600.

This is a useful tip when you are trying to do some quick calculations in your head.

Not a good idea, you'll make 144$ in a week. The week after that difficulty will rise and dismantle your prognosis.

difficulty @ $8.50/btc = 220000

difficulty @ $18.50/btc = 520000

Would you rather make 1 btc a day and it's worth 8.50 or half of a btc per day and it's worth 18.50.

See what I'm getting at ?