According to Associated Press writer David Crary, "...the Census Bureau says same-sex couples in any state who consider themselves spouses should feel free to check the 'husband' or 'wife' boxes on the census form, rather than 'unmarried partner'." In defending this cockeyed policy, Tim Olson of the Census Bureau pointed out that they don't ask straight people to produce their marriage licenses. Perhaps not, but they also do not encourage unmarried 'straight people' to lie about their legal marital status.
Besides all that, most people don't seem to know that the constitutional purpose of the census is to determine how many representatives each state gets in Congress (and by extension, how many electors). It is not to find out how many bathrooms your home has, whether you are gay or straight, how many teachers to hire, or how much money a community gets.