The real tragedy of the Supreme Court's ruling on the "Defense of Marriage Act" (DOMA) is that the government is still attempting to engage in social engineering — both by subsidizing and financially incentivizing marriage and by trying to define it. Government should treat every individual as exactly that: an individual and nothing more. Adjusting someone's taxes or benefits based on their relationship status is improper and discriminatory. Today's decision did not end government discrimination by any means; it merely moved one small group into the protected class. Elevating some relationships above others is not the proper role of government no matter how broad or how restrictive the definitions may be.
A "marriage" (by whatever definition) is not any more deserving of government recognition or subsidy than any other relationship including those of platonic friends. The truth is that friends may cohabitate and married couples may live apart. There is no practical definition of marriage other than that it is sanctioned through the issuance of a government license (and the payment of an associated fee.)
Government should not attempt to define relationships at all, and it certainly should not use its taxing power to reward some and penalize others. Today's decision only serves to reaffirm the government's intent to meddle unnecessarily in the lives of individuals by stripping them of their individuality and categorizing them into arcane, capricious, and discriminatory categories.