Approval Rating Nonsense

So, according to Gallup, President-Elect Obama has a 70% approval rating. To preface: I'm a huge stats dork. I currently have a man crush on Nate Silver (update: and apparently I'm not the only one). That said, what the hell does a 70% approval rating even mean? I hate to emphasize the bleeding obvious but, he's not president yet. What performance do these people approve of (or put a different way, what do the 30% disapprove of)? It reminds me of the stupidity of preseason rankings in college sports. Wait until the man gets into the game to judge how he's doing.