Divorce settlements would be worked out in court the same way that hetero couples do it. So that's out.
Why shouldn't they be able to file joint income tax returns if they are legally married? The break is meant to make life easier for married couples to start a family, so why wouldn't it apply for homo couples? Married hetero couples who don't plan on having or adopting kids take advantage of the tax break too, so any argument claiming homo couples would be taking advantage without adopting is out too.
Family rates on health insurance? OMG! Next they'll take advantage of family rates at every business that offers them including the Shoney's salad bar! OMG! Hahaha. If I'm not mistaken, I think insurance companies give breaks for everything, including how many kids you have or if you're just plain married. But if they are married under the law, why couldn't they take advantage of things like this?
"Next of kin" stuff can already be decided in living wills and things of that nature, but why wouldn't a person be able to make decisions in the stead of their spouse? Afterall, they are spouses. What's different here other than the fact that they're both the same sex?