I thought Stephen Colbert's Twitter post was great: did you know a gesture can have two meanings? i.e. in japan bowing is a sign of respect but in the U.S. it's a sign of a weak president
Even the State Department has a policy that says to respect the culture of the country you're in when giving greetings. Per AP article: In an online State Department posting from 2007 titled "Protocol for the Modern Diplomat," envoys are advised to be aware of greeting rituals such as kisses, handshakes or bows and to follow a country's tradition.
So to anyone who was offended at Obama bowing to another world leader - go take a nap and chill out. And please let those of us who are aware and respectful of other countries' customs be the ones who truly represent our country to the world.