Personally, I've always thought that the best solution to this controversy is to abolish marriage altogether (straight or gay) as it relates to the state. The only reason the government should be in the business of legitimizing what is essentially a matter of interpersonal relationship is to regulate the raising of children, and if we eschew that particular justification (and I believe we have), then I just don't see another good one out there. Should we be able to privately contract for so-called marital privileges? Of course. With respect to property, social security, etc., you should be able to assign your rights any way you choose. But letting marriage be the defining factor in that right rubs me the wrong way.
The question I would like to ask the Supreme Court of the United States is whether we have a right not to be married under the doctrine of substantive due process (14th Amendment). Apparently we have a right to consensual sex (between adults), a right to use contraception, and a limited right to abortion, all under the umbrella of the "right to privacy." But do we have a right to remain single? If so, is it unconstitutional for the government to discriminate against non-married people by conferring special rights to married individuals? I think it does.
Perhaps I should start writing that brief right now.