THE BAD NEWS for newlywed Massachusetts gays and lesbians is that, under the 1996 Defense of Marriage Act, the federal government won't recognize their marriages. The good news is that by staying "single" in the eyes of the Internal Revenue Service, they could save a lot on taxes. Despite some reforms in 2001, many two-earner couples still pay a "marriage penalty," particularly if one spouse earns enough to hit the top tax bracket on his or her income alone. Same-sex couples are more likely to have dual incomes than heterosexual married couples. In Massachusetts, both partners work in 66 percent...