Do your hands get cold in the wintertime? Well, you could get a pair of gloves. Or you could get Sanyo's Eneloop Kairo hand warmer, load it up with batteries and hold onto it tightly.
Basically, these things are like those heating pads designed to go in your boots and gloves, only battery-powered. It's kind of like taking the bottom of your laptop and putting it in the form of an egg. for $45, I'll stick to mittens, thanks.