Jesus had a lot to say about empire.  None of it was positive.  The United States of America is as much an empire today as Rome was at the time that Jesus made those statements.  Jesus made it clear that His kingdom is not of this world.  He also had a lot to say about loving your neighbor and even loving your enemy.  So, I find pledging allegiance to an earthly kingdom misguided at best and idolatrous at worst.  But, it is not something that I can do in good conscience, as a follower of Christ.  I have not been able to say the pledge of allegiance in good conscience since I was in junior high.  Nobody noticed until high school, at which point a teacher asked why I stood but stood in silence and refused to place my hand over my heart or recite the words.  I explained to her that to profess allegiance to a piece of cloth (no matter how noble what that cloth represented was meant to be) or a country (when I am a human being and have a love for every human being, whether they exist within the same borders as I reside within or not) is not something that I could do as a follower of Jesus and I was not going to speak an oath to appease anyone.  She sighed and left me alone after that.  I was not being disrespectful... I often stood during the pledge.  It was simply a matter of conviction for me.  I wrote a blog entry on this issue a few years ago that included some research and information that I "gleaned" from someone else who had written more extensively on the subject.  That can be found at http://www.myspace.com/theshadowpoet/blog/326868815 if anyone is interested in some of the more in depth reasoning behind my convictions.