I looked back at my past year's worth of bills and saw that I used a total of 3648 kW-h. I'm not sure if that's good or bad, though each month my power company sends me a notice that states I'm using about 15-25% less energy than my energy efficient neighbors. I live alone in a house that's bigger than I need but not ludicrously so, and I don't tend to leave computers running. As 30-year old appliances fail I've been replacing them with more efficient models, and as they burn out I'm replacing incandescent light bulbs with CFLs (but dang, some of those daily-use incandescents are over 12 years old at this point, I'm beginning to think they'll never fail).
The big surprise for me, however, was my bill from last January; my electric energy use easily outstripped even my summertime air conditioning use, and was a fair bit higher than the months immediately before and after. The bill kindly informed me that the average temperature that month was 9 degrees colder than the year before, but I couldn't see that making such a huge difference. Could it be the air circulating fan in the furnace that I let run on low most hours of the day? Maybe, but why the anomalous month? I considered a incorrect meter reading, but realized that it's read remotely rather than by a guy walking around the neighborhood, and any mistake would have been offset the other direction the next month. Then I remembered.
For occasional use by my houseguests I have one of those oil-filled radiator-styled space heaters in my guest bedroom. I recall that sometime in that December-January timeframe the heater was used, and I forgot to check that it was turned off after a houseguest left. It sat there maintaining a comfy temperature in the otherwise unused bedroom for approximately a month before I happened to enter the room and noticed.
So now I know just what an energy pig that space heater is, and I'll be extra careful to check in on it after houseguests depart. Thanks Slashdot, you've probably saved me several tens of dollars over the next decade as I become more vigilant about the heater's use.