Overwhelmingly most of it. Most generators run on diesel and not gasoline, and I gave up trying to figure gallons per KwH after a few minutes of googling. But you're talking about converting heat to mechanical energy with a ton of lossage, and then mechanical to electricity with a ton more lossage.

The original article isn't interesting. You may as well say that your mouse has enough energy to recharge your iphone for 10 years, provided we found a way to convert the mass into energy.

But the way to turn fuel into energy already exists, even if it is inefficient. OK, you could also burn my mouse, but it would probably be even less efficient...

I still think it makes a strong point for telecommuting.