We turn off all our pc's at night except for one, which monitors several sites 24/7. However, that pc has to be cold-booted at least once a day to reclaim all the memory that gets sucked up during daily operation (in addition to the site monitoring). I've found that cold-booting completely handled constant crashing that warm reboots did not take care of. Having 4 pc's running makes the room around 10-15 degrees warmer than the rest of the house, which is, to me, a definite indicator of the amount of electricity being used. So we turn off the other 3 at night.