I completely and totally understand Vince's point of view in this situation. For someone of another culture to use a representation of their religion over the Bible for the purpose of affirming an oath of office seems a little offensive or, perhaps, disturbing given the fact that he is Muslim and all the criminal connotations that seem to go along with that religion these days. Personally, I believe in the Bible and what it says and wouldn't dream of taking an oath upon anything but.
HOWEVER, just as there are different cultures in the world, there are different religions right within our country as well. Catholics don't believe everything that the Lutherans believe. Protestants don't believe everything the Presbyterians believe. Methodists don't believe everything the Pentecostals believe. My point is, we ALL take the oath on the same Bible. It doesn't take away from the significance of the Bible at all. Our interpretation of its content is what makes it sacred for all of us.
I have to assume (since I'm not of that faith) that the Muslims feel the same way about the Koran. And as someone eloquently stated previously, if that makes him comfortable and he considers the content of the Koran to be sacred and will help him uphold his duties in office, then go for it.
Think of it this way, if I was taking an oath of office and someone placed a Koran in front of me, do you think I would take them seriously? No way. It is totally meaningless because that's not the religion I practice. However, put a Bible in front of me and you can be assured that I will uphold my position to the utmost highest standard.
Just my personal observation...