Wel fired is not possible. I own these machines. Secondly, I'm already paying costs for people leaving them on.
Sure, but, with respect to your electricity bill, being on and not doing anything is different than being on and working at 100%. Say you use 100 machines. If each of those machines did 5Mhash/s then you'd get 500Mhash/s from the whole lot. Let's say that each machine only draws 100W at full load. That's 10,000W for 500Mhash/s. Now compare that to my single 6990 GPU system which draws 500W and does 780Mhash/s. Those 100 systems would use 20x more energy than my 1 system but would produce fewer bitcoins.