Electric blankets are not inherently evil. They can actually save you energy by allowing you to turn your thermostat down a lot farther than you otherwise would. Just take the following precautions to limit your blanket's electricity use and maintain safety.
First, turn it off in the morning. (I'm sure your cat enjoys having a nice warm bed to curl up on at two in the afternoon, but you really don't need to pay the electric company to keep Tabby happy. Get her a catnip mouse instead.) If you might forget to unplug the blanket, get one with a timer control that turns off automatically.
Second, you might want to pile another blanket or comforter over the electric blanket to hold more heat in your bed. Before you do this, though, be sure to check the instruction manual: if the instructions say not to do this, don't, it's not worth the risk of ruining the blanket or starting a fire.
And while we're on the subject of safety--if you or a loved one has an electric blanket that's old (especially if its over 10 years old), damaged, or frayed looking, replace it! (See more safety tips here.)
To maximize both energy efficiency and safety from an electric blanket, pay close attention to all information you receive from the manufacturer. After reading the instruction manual, definitely fill out and mail-in the warranty card so they can contact you if additional information is released about your blanket.