It's been a two year project. We live in Phoenix in a nine-year old home. Two years ago our power bill was $173.00/month with the utilities monthly average payment option. First, the seven year old air conditioner, which was showing signs of dying in late May, was replaced with a Trane XLi 19 (the 19 SEER unit), new air handler and new furnace. That cost $8,000.00, but comes with a complete 10 year guarantee. The HVAC company had guessed I was getting about a 7-8 SEER from the old pile of junk, so that made a huge difference. This year we replaced all the windows and the patio doors that were poor-quality dual pane that was leaking badly. All new vinyl windows and a new patio door (w/argon gas and Low E coatings that come with a complete double lifetime warrany) for a price of about $4,500.00. Next, all new upgraded appliances that are all Energy Star rated. About $6,000.00. Finally, all lights replaced with florescient fixtures, lamps or bulbs.
The bottom line is that the power bill has dropped from $173.00 mo. to $83.00 mo. The liveability of the house, as well as it's resale value, have greatly increased. There were tax credits that have been, or are-to-be, applied that reduce the net expenditures. There is one thing that I do that helps a lot but other folks may not be willing to do and that is to set the thermostat to 85 degrees in the summer. At night it goes down to 81. Remember that it is usually fairly dry here in Phoenix and that it is far easier to take higher temperatures then in other areas of the country.
One last parting thought. It is the old axiom that you can pay now or you can pay later. Energy bills do not return any long term value to the house or your lifestyle. Once the money is spent it is gone and has no residual value. However, upgrading saves money and increases both the enjoyment and the value of the home. So it isn't a strict apples-to-apples comparison of the costs of upgrading vs. the cost of the energy bills.