At some point in the not-too-distant future, there's going to be a case involving a pair of Massachusetts residents who got married and later moved to another state.We're still waiting for that situation to come up. But a case that already has come up suggests to me that we won't have much longer to wait. Two women from Connecticut got married in Massachusetts (presumably because the governor had yet to order clerks not to issue licenses to out-of-state same-sex couples). Then, back home in Connecticut, one of them filed for an annulment. The Connecticut trial judge held that she lacked jurisdiction over the petition. The reasoning is a bit complicated, and I'm not sure it actually makes sense. But the gist of it is that there was no "marriage" over which the family court could exercise jurisdiction: the Massachusetts statute banning out-of-staters from skirting their home-states' laws meant that the marriage was void from the start, even under Massachusetts law.
This is only a trial court decision, and unless the SJC strikes down the statute (which I think it won't), the decision does not put Connecticut in conflict with Massachusetts. The more difficult situation, which will put the constitutionality of the federal Defense of Marriage Act and various state laws directly into question, will be when a couple with a legal Massachusetts same-sex marriage ends up in litigation in another state.
That shouldn't take long. As the Connecticut case emphasizes, a percentage of marriages fall apart within months. I think the odds are that we'll soon see at least one member of a same-sex couple move out of Massachusetts and file for divorce in another state.
And that's not the only fact pattern that would put the constitutional questions in issue. For instance, say one spouse is killed in an accident while on vacation in Florida. The surviving spouse might sue the person who caused the accident in Florida court, and the defense would certainly argue that a same-sex spouse can't bring wrongful death or survivorship claims under Florida law; to which the plaintiff would certainly respond that the Full Faith & Credit Clause requires Florida to accept the validity of the Massachusetts marriage and that anything in DOMA or Florida law to the contrary is unconstitutional.
I expect the pending SJC decision to get a lot of press when it comes out. But the truly significant cases will come from courts in other states.