light bulbs: turning it off and then on again costs more energy than leaving it on for a short time. (I forget what the actual time threshold is offhand.)

IIRC, it's around 30 minutes for an incandescent and 2 hours for standard fluorescent. This is supposed to include the energy costs of manufacture vs the increased wear-and-tear. I don't have a citation handy, and I don't know how modern compact fluorescent bulbs change things.