Tax Complexities for Same-Sex Couples

The Internal Revenue Service has decided same-sex couples in California (and maybe other states) should treat their income as community property, reports The Wall Street Journal: "Couples who are registered as domestic partners in California must combine their income and each report half of it on their separate tax returns."

Note the reference to separate returns. "Same-sex couples, even if they are legally married in their home states, may not file joint federal tax returns. The federal Defense of Marriage Act, passed in 1996, defines marriage as between one man and one woman and bars federal agencies from interpreting it otherwise."

Will estate lawyers and accountants have related complexities to deal with when the federal estate tax revives? Could an "all-to-spouse-or-partner will" have one tax result in California (thanks to community property) and other in Massachusetts (where everything would be taxable in the absence of a marital deduction)?