When Is The Best Time To Start Heating Your House?

I made the phone call today. The dreaded one, to the oil company. Just 100 gallons though please, because if I fill the oil tank, then I don't eat for a week. Two days ago when I woke up, it was 58 degrees in the house. But I didn't give into temptation and fire up the ol heater and wake it up from its summer slumber.

What is your threshhold? Do you set a date and wait till then to use the heat? It is a temperature thing? Or have you already cranked up the heat this season?