I saw this on the Lemon Fools "living below your means" board. Thought I'd re-post here as it might be of interest to someone: www.lemonfool.co.uk/viewtopic.php?f=14&t=36028
Don't think you have to register to view, but I've also done a screen-shot.
Summary - someone's wife works from home in a cold room. He got her a heated car seat cover
www.argos.co.uk/product/7065567
with adaptor so it can be plugged in
www.halfords.com/camping/coolboxes/halfords-coolbox-mains-to-12v-accessory-adaptor-290806.html
Apparently it's very warm and costs about 1p for 4 hours to run.