“The rule of thumb is that you can save about 3% on your heating bill for every degree that you set back your thermostat” full-time, says Bill Prindle, deputy director for the nonprofit American Council for an Energy-Efficient Economy (ACEEE). Turn down the thermostat 10 degrees when you go to work, and again when you go to bed — a total of 16 hours a day — and you can save about 14% on your heating bill, says Prindle.

If you own a home and you don’t have a Programmable Thermostat you are spending money to heat a home when you don’t need (or want) to.
A decent Programmable Thermostat can save you $150/year on natural gas – easily offsetting the cost for purchasing it.
The key to purchasing a good Programmable Thermostat is to look for the number of days you can program. Most are coded in the following maner:
5-2 Allows you to setup a program for Mon-Fri and one for Sat-Sun.
5-1-1 Allows you to setup a program for Mon-Fri, Sat, and Sun.
7-day Allows you to setup a program for each day

Another item to consider is the number of periods per program you have, generally most offer 3 or 4 periods which can generally be divided up like this:
3 periods: Day, Evening, Night
4 periods: Morning, Day, Evening, Night

Due to my families schedule and for maximum expandability I purchased a 7-day, 4 period Programmable Thermostat.
This allows me to setup my week like this:
Workdays (Mon-Fri are identical currently, will change when the wife starts working part time):
4:45am – Morning (we get up at 5:am), hold at 67 Degrees
7:00am – Day (we’re at work) Hold at 60 Degrees
4:15pm – Evening (we’ll be getting home soon), hold at 67 Degrees
9:45pm – Night (sleeping), hold at 60 Degrees

Basically, when we’re away or sleep we have no need to keep the house warm. Why pay for natural gas when we’re either not around or asleep under some nice thick covers? I’m thinking about knocking the day time temp even lower – like 55. We can always adjust the temperature if needed.