The Census Bureau does not ask questions about sexual orientation. However, responses to some questions provide data about same-sex couples. This data should not be used to draw general conclusions about gay/lesbian/bisexual Americans, but when handled with appropriate care, may still be useful for reporting.
Table B11009, Unmarried-partner Households by Sex of Partner, is the only table which provides information about people who have told the Census Bureau that they live with a partner of the same sex. As explained in the Census Bureau's Frequently Asked Questions About Same-Sex Couple Households document, responses reporting a spouse of the same sex as the house holder are changed to indicate an unmarried partner, regardless of state laws permitting same-sex marriage.
Consult the Census Bureau's documentation for more details. Specifically, American Community Survey Data on Same Sex Couples provides national-level data on the household characteristics (including income, education, etc) of same-sex couples compared to married and unmarried opposite-sex couples and married couples dating back to 2005, as well as more data and methodological details.