This is actually a pretty neat idea. If you're on a plane and aren't sitting in business or first class, you probably won't have a plug to power your devices (mp3 player, gameboy, any small device with a USB charging cable).
So this little bugger plugs into the headphone jack. Turn the volume all the way up and it'll start to store the energy coming out of the head phone jack. O_O
Granted there's not a lot of power coming out of a headphone jack. It says that it needs 3-5 minutes to power a USB device for 1 minute. Obviously that's not enough juice to power your laptop.
It's better then nothing right? And hell, it's a lot cheaper then flying first class.
I might get this on my next transcontinental flight to China or Japan. I mean my DS lite will last for 6-8 hours but flights to Asia are 12-14. And I already ordered a USB charging cable for the DS lite. O:)