Update: There are some questions about the credibility of these folks. (And this.) Before my original post I did some brief checking and it seemed legit, and it still appears as though this is a real issue that we should take on, but perhaps the Invisible Children organization is not quite as straightforward as it first appeared.
Update 3-12-12: Invisible Children responds to critics with this video.
Update 3-14-12: And another critique. And more response.