The New York Times has a good article about the tax headaches faced by same-sex married couples in California, Nevada and Washington, where special “community property rules” apply.  An IRS ruling in 2010 allows same-sex married couples in those states to calculate their federal taxes in the same was as opposite-sex couples.  Most people considered the ruling a step forward for same-sex couples, but as the article points out, it is also a source of headaches and confusion.