Two of the computers are on all day. One runs our internet and server so its up 24/7 but it has no moniter. So that helps. The rest are always on but they go into "sleep" mode if no one touches them for ten minutes or so. I think they take up about a vcr clocks worth of energy in sleep mode...but that could just be hearsay.
And yeah reptiles and fish aren't good hobbys for those wanting to have cheap hydro bills!