David Roberts covers three basic rebuttals to the charge that Gore talks the talk but doesn't walk the walk. The first two I think are legitimate (assuming their factual basis is correct):
1) Gore does not actually use that much energy, and the energy he does use is green. Obviously if he does in fact walk the walk, the hypocrisy charge evaporates.
2) Gore's extra energy use is necessary for him to spread the message about climate change, which ultimately results in greater conservation. This is a standard consequentialist tradeoff argument. I think insistence on personal purity is morally questionable across the board, but it's especially so with respect to a fundamentally consequentialist issue like climate change.
But Roberts says he wishes he could focus on a third argument -- and in fact it seems to be the most popular argument among Gore's defenders:
3) Gore does so much good work on this issue that he deserves to be allowed to be a little wasteful in his personal habits.
The problem is, argument 3 is not a valid one. It essentially says that the more you talk the talk, the less you need to walk the walk. Can you imagine anyone saying "you know, Mark Foley did so much good chairing the House Caucus on Missing and Exploited Children that he deserves to hit on a few pages. He earned it!" Of course not.
The overtones of argument 3 -- which I'm sure Roberts and others would deny intending, but they're there all the same -- are also troubling. It implies that Gore is a better person than us peons, who's too important for us to be worrying about whether he walks the walk. And it plays into the conservative frame that environmentalism is all about sacrifice, so energy use is like an ice cream cone that you'll give up if you're good, but you can have as a reward if you're a good boy.
So maybe Gore doesn't use all that much energy, and maybe his excessive energy use is a necessary cost that's offset by the benefits it allows him to achieve. But it shouldn't be some sort of reward that we should give him for being such a great activist leader.