There are several layers of problems to be overcome.

At the state level, where marriage laws are enacted, voter sentiment is against legalizing gay marriage. Nothing new there. We all know this. In the few states where gay marriage or "civil unions" are permissible, they exist as a result of legislative actions or judicial decisions. Correct me if I am wrong, but in most (all?) states the issue has been put on the ballot for voter approval, it has been defeated. So, it will be a long time coming before a significant number of states grant "civil union" status. Much longer still, imo, to have many states approve gay marriage. Then what?

At the federal level, which I think is where the "quickest" route to any serious change lies, there are laws like the Defense of Marriage Act, (which I believe states a marriage is between a man and a woman) and the big bully, the Internal Revenue Code. One need not look far into its pages to find the applicable law:

Code Section 1.
"There is hereby imposed on the taxable income of—
1(a)(1) every married individual (as defined in section 7703) who makes a single return jointly with his spouse under section 6013, and
1(a)(2) every surviving spouse (as defined in section 2(a)),............"

And the regulations thereunder:
Regulation §1.1-1.,Internal Revenue Service,Income tax on individuals

For the computation of tax in the case of a joint return of a husband and wife, or a return of a surviving spouse, for taxable years beginning before January 1, 1971, see section 2. The computation of tax in such a case for taxable years beginning after December 31, 1970, is determined ...........

So, the IRC says "married individual" and "his spouse". The regulations say "husband" and "wife". Different words. Same meaning.

Until the law is changed at the federal level, what Mass. or Vt. or Iowa or NJ do is nice, but it's not even "half a glass". The path to total change has begun in California. We discussed this in another thread a while back. This case will end up in the 9th Circuit. Whoever loses will appeal to the Supreme Court. If they hear the case, and if they rule favorably on gay marriage, then that be that.
Finally, any federal change will come from the Court. Hell will freeze over before Congress approves gay marriage (or a proposed constitutional amendment on it.)

We had a lot of hot air on both sides of this issue in NJ for the last couple of years. Our now gone Governor supported the legislature in trying to pass a gay marriage law on his way out the door. It didn't come up for a vote, despite both houses in NJ being decidely democratic.

I've wondered for a few years at least, why they didn't back door this by changing state laws to get out of the marriage business altogether and call everything civil unions. But I suppose such a step might imperil their citizens' rights vis a vis the many federal laws dealing with "marriage" in one way or another.

Enjoy doing what you want to do.
Illegitimi non carborundum