I had a problem. The problem was that it was too hot at night, but too cold in the morning in my rented condo. I built a contraption to turn the fan on and off using a Lego NXT and linear actuator.
Mechanical parts for version 2.0 were printed by Shapeways. An arduino with a pololu motor controller and an RTC module from sparkfun were attached precariously with zip ties.
I now live in my own house with my very own programmable thermostat.