[quote=Halo]
I saw a statistic somewhere or other claiming that $17 million is spent daily in electricity bills in order to mine $4 million worth of Bitcoins, because of the ridiculous amount of computing power needed to crack the algorithms at this point. Not sure about the accuracy of the data, but it's food for thought.
[/quote]

This is, firstly, because Bitcoin has become incredibly difficult to mine. More importantly, bitcoin is incredibly volatile. That 17-4 ratio you cite could very well be accurate (I'm drunk and can't be assed asses the veracity of the statement), but the people who invest in the hardware believe that bitcoin might at one point become valuable enough to warrant the expenditures. 

Keep in mind that the average doesn't apply to people running ASICs. These dedicated bitcoin miners have a much lower ratio of value mined to expense. These people likely believe that bitcoin will grow in value, that is, that the future price of bitcoin will outweigh the current price to generate.