Right...that was the entire point to DOMA. If Mass. manages to force the feds to recognize gay "marriage," then DOMA will die and that will kill all the state constitutional definitions of marriage.
But that could open all states up to recognizing the laws of all other states. Like I mentioned before, some states could be forced to allow conceal carry permit holders from one state to carry in any state.
The most scary part of it is though, that it sets the stage for the federal government to start making "standard" laws for all states.