For the average person using a desktop or laptop, an hour of computing can use about 2-5 watts of electricity. On average the typical American home uses 980 kWh per month for 365 hours.
So an hour of computer use will be about 5% to 18% of your monthly energy usage. If you are having trouble keeping your electric bill down, one thing you could do is upgrade your monitor so that it has a power-saving mode which will help reduce how much power it uses when not in use - especially if you have your computer on 24/7. Another small change might be getting a cheaper printer, but just something to think about when you're weighing all options for reducing utility costs!...