One of the wackier aspects of the anti-gay-marriage amendment--because 1) lawyers are a perverse and twisting breed, and 2) the amendment was written as stupidly as possible so that it couldn't be discomprehended, it could be argued that it invalidates all marriages.
has more details, but it boils down to "Let Marriage = X, but all cases of X are invalid." Now, the spirit of the law assumes that Marriage is the only valid case of X, but it would require only minimal stress to the law to create a bad technicality for some, oh, say, commonlaw couple.
Aaanyway...please vote! And please encourage other people to vote :)