Interesting question -- my wife and I live in an 1800 sqft home in Florida. (Bigger than we wanted, but the 12-1300 sqft houses that were bikable to work were in lousy neighborhoods.) We typically use between 350 and 500 kwh per month @ $.09 per hour. Surprisingly (to me) we don't spend much more in the summer. The real spikes tend to be when we have guests. In the summer, we keep the house at 78 or 79 overnight, then bump it up to 81 when we're out during the day. We've got ceiling fans and it's a cinderblock house with plaster walls (hence decent thermal mass). In the winter, we keep the house at 68, but that only kicks on for a couple of weeks, usually. In all, our bills are usually between $50 and $65, with occasional spikes as high as $80 (again, usually when we have guests).