I never really have understood how energy distribution and payment works. No matter who you pay (and it's a monopoly here, so I understand it better here), you're getting your energy from the same grid. Duke Power, Progress Energy, Green Mountain, etc. all just put energy on the grid. There's some sort of payment system between the companies so that if Duke Power needs more than they can provide, then they pay Progress for it, for example. To me, this means that if enough people start paying Green Mountain, to the point that their customers subscribe to more than they produce, they have to buy power from someone else who is not "green". And if they don't have enough customers, another power company will buy their surplus. (One of the things I don't get is how they make sure that the right amount of power is on the grid.)

So I'm happy that there's a company that's producing cleaner power, though I imagine it's relatively little of it, but I don't quite get how using them as your power company will make anything any better.