This story too by itself means little. No doubt Obama was tired or as Mark puts it:
Maybe he's been hearing it five times a day, every day, for the last year, and this time he forgot to salute. Maybe he was doing something else when they started playing—carrying a brief case, shaking hands with people in the crowd—and he just didn't go into "national anthem mode."
The effect of these things is cumulative. Combine them with his odd name (Barack Hussein Obama), his education in Jakarta and so on and you get the sense...well, you get the sense that he's not one of us. You can't say that about any of the other major candidates (well, maybe Romney-I guess it depends on how you feel about the whole Mormon thing).
I wish Obama well. He seems like a decent guy and I don't doubt he has a bright political future ahead of him. Running for President is hard work and unfortunately there are times when he acts like he's...unserious about the whole project.