Same-sex married couples won't be counted as married couples in the 2010 census.
The Census Bureau does not ask about sexual orientation, but it does ask people to describe their relationships to others in their household. If a respondent refers to a person of the same gender as their "husband/wife" on the 2010 census form, the Census Bureau will automatically assign them to the "unmarried partner" category. Legally married same-sex couples will be indistinguishable in census data from those who chose "unmarried partner" to describe their relationship. [Link]