While running Bitcoin mining on your fast GPU ATI hardware you may want to know how much it earn you in next days or weeks. For this purpose you may want to check some Bitcoin mining calculators.Bitcoin wiki got a page with link to all popular calculators around the net for today. There are two most popular - Generation Calculator which can compute how much would you get American dollars (USD) in day, week or month based on your hardware hash rate and market exchange rate of 1 BTC.
The second one will show you more information about current state of the Bitcoin network and future changes in mining difficulty. This gives you more accurate assumption on your earnings in the future, which will be lower while difficulty rises.
As you can hear MtGox is big bitcoin exchange and it got hacked last week. Exchange admins said database was leaked with password hashes. Some of weak passwords were computed and hackers started sell-off bitcoins and excahge rate down to 0.01 USD for BTC. Admins stopped operations on the site and promised rollback all hacked transactions. A few hours ago MtGox went back online and started transactions. Current prices are 17.5$ per BTC.