Why does the government insist upon recognising marriage status in the first place? It seems like it would be better for all parties involved if the marriage tax penalty was repealed and the government took it's hands off the issue entirely. Employers could dole out benefits as they saw fit, child custody could be settled like it is now (or biologically if it came down to it), and joint ownership issues in case of divorce could be resolved by prior encompassing contract.
Keep marriage for those who choose it as a traditional, ceremonial, or non legal personal/religious commitment. No need for the government to allow/disallow homosexual unions in the first place, or hetero ones for that matter. Everybody's happy.