I'm not quite a skeptical as you about all polls. Ones that are well-done can provide valuable information if their limitations are understood. Political parties wouldn't pay big dollars for them, otherwise. These private polls don't want a particular result, the ones paying for it want to know the truth, even if it is painful. Results from the good, private polls generally aren't publicized so as to not alert the opposition. Most media polls are junk because the ones paying for the poll want results which can be spun into a storyline.
Media polls right now reflect little more than name recognition. Given that Mitt is the best known of the announced candidates, I'm not surprised that he is leading right now.