The US Census apparently has already decided that *legal* same-sex marriages in California and Massachusetts will not be counted in the 2010 Census. Instead:

The U.S. Census Bureau, reacting to the federal Defense of Marriage Act and other mandates, plans to edit the 2010 census responses of same-sex couples who marry legally in California, Massachusetts or any other state. They will be reported as "unmarried partners," rather than married spouses, in census tabulations - a policy that will likely draw the ire of gay rights groups.

I'm not sure why the federal DOMA hasn't been challenged yet in court. It would take a couple getting marriage in MA or CA and then moving to another state to ask for their union to be recognized. The Full Faith and Credit Clause of the US Constitution states that:

Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State. And the Congress may by general Laws prescribe the Manner in which such Acts, Records and Proceedings shall be proved, and the Effect thereof.

This has always been interpreted around marriage to mean that marriages performed in one state must be recognized by another. Time to knock DOMA out. It's unconstitutional and mean-spirited. There's no two ways around it.