I hate it, when listening to arguments about why same sex marriage should not be allowed, when the "traditional meaning of marriage", or the "biblical meaning of marriage" argument gets brought up. The "traditional" meaning has changed with time (and place), and our conception of marriage today is quite different to the biblical concept (polygamy anyone?).
On that note, here is a post by Victoria Adams, who, as an anthropologist and Christian, breaks down some of the history of marriage, both in the Western/Christian tradition, and in other world cultures, to show how the "traditional/biblical meaning of marriage" argument simply doesn't hold water. Read it.