With all the back and forth over what Dubya has proposed, I thought it would be beneficial to look at the proposed amendments (Disclaimer for the humor and satire impaired: despite the address, I believe it is satirical). And here's more info from the definite source of the definition of marriage.
I hope to have more to say on this matter, meanwhile, check out dis and dat where I've talked about it before.
Update: Actually, after thinking about it, those links above pretty much cover it. But I forgot this link, also. And, as John Stewart said on the February 24th edition of The Daily Show, the last time an amendment was put in restricting something, it was Prohibition, and you know how well that went. The problem disappeared, and it became known as the Sober '20s.
Update Updated: Wil Wheaton posted his thoughts on the matter. I'll be adding good links as I encounter them, so keep checking this entry for the next day or two.
Here's one debunking marriage myths.