In a perfect mining market the total amount of money spent by miners each day (cost of electricity/bandwidth + amortized cost of hardware) will always tend to c

In a perfect mining market the total amount of money spent by miners each day (cost of electricity/bandwidth + amortized cost of hardware) will always tend to converge on the value of the mining rewards (minus some profit margin), which for the next 4 years is about 3600 BTC per day (25 BTC/block * 6 blocks/hour * 24 hours/day). If the value of Bitcoins go up, so does the number of miners securing the network, which makes sense. It's pretty ingenious.