My immediate response was "surely this is less than the cost of the electricity to run the CPUs" but it turns out it's equal to the marginal cost of heating a r

My immediate response was "surely this is less than the cost of the electricity to run the CPUs" but it turns out it's equal to the marginal cost of heating a room with CPUs relative to conventional heating (natural gas or electricity) -- which is pretty genius. In the long run you would expect this would drive up the bidding for idle CPU time, meaning that having a couple of idle computers in your house would generate you a small amount of positive revenue, in much the same way that contributing electricity back to the grid using solar cells could. Of course, most people have no use for solar cells (which are expensive), whereas a lot of us have use for local CPU.