Bitcoin mining isn't financially viable in Australia due to high electricity costs to run the equipment. You really have to be at the bleeding edge of the price/performance curve to make money mining these days. Bitcoin mining is now being concentrated in China due to the low costs of electricity. But that being said, it will always be viable for someone until the last coin is found due to the dynamic nature of the difficulty to find a block and get some coins. The bitcoin system periodically and pre-determindly checks to see how long it takes to mine a block. The bitcoin system wants it to take about 10 minutes to decrypt a block. So, if more and/or faster equipment starts mining, the difficulty goes up to maintain a steady pace. If miners stop, the difficulty decreases etc.
