First off, the challenger always has an advantage in the first debate (well, all of them, but a big one in the first). The incumbent has a record he has to defend and is a known quantity (which can be good and bad). The challenger is more or less only known to the majority of the public based on political ads and some sound bites. Debates like this are the first time most voters have had to actually hear the challenger speak in his own voice. All he has to do is come off like a person and not some evil goblin like his opponent has been painting him, and he wins.
This was more than that level of win though. Much more. Obama simply was not prepared for the debate while Romney had a response for every single thing Obama said. About half way through it looked like Obama came into this just thinking he could regurgitate the same talking points he uses in his speeches and TV ads and everyone would fall over themselves agreeing with him. I suspect he's gotten too used to being the only person in the room with a microphone and/or fielding softballs from a friendly media and forgot what an actual debate requires. So when he did toss out those talking points and Romney was ready with a strong response, he basically didn't have anything. Near the end, when Romney stomped him on the energy deductions/subsidies thing, Obama was looking at the floor with a half grin on his face just kinda shaking his head. That body language alone spoke volumes. It screamed "Yeah. You caught me fibbing". And that's not what you want in a debate.
There was no knock out punch, but Obama still took a pretty good beating. He did way way worse than I expected. What I found really encouraging (from my perspective at least) was that when Obama was talking I was making mental notes about how Romney should respond, and with a couple exceptions he answered with about the same counter argument I was hoping for. From the sounds of some of the posts here, most liberals spent the evening screaming at the TV saying "Why didn't he counter with this, or say that?". So at least from a "getting his position across", Romney certainly did better. I honestly think that this was lack of preparation. He just wasn't ready for Romney to have answers to his points. I suspect that's also why he didn't bring up the 47% thing. If he wasn't ready with a counter response, he would just be giving Romney a platform to clarify his statement and thus nullify its value in the campaign. It's much more useful in political ads than in a debate.
Dunno. Obama just came across as a guy with a bunch of talking points he couldn't defend. Whether you agreed with Romney's answers or not isn't the point. He had them and that made him look like he knew what he was talking about. Also, as Smash pointed out earlier, it's Obama's job in the debate to counter statements Romney made that he thought were inaccurate. A group of people who are already going to vote for Obama jumping up and down and posting on their blogs about how Romney was wrong because of X, Y, or Z doesn't undo the fact that when Obama had the opportunity to say that in front of voters who don't visit political blogs he failed pretty much completely to do so.
Oh. And for the record, I'm also looking forward to the Ryan/Biden debate. That should be "interesting" to say the least.