New York's legalization of gay marriage simplifies one major issue: In that state, same-sex couples have the same marital rights as opposite-sex couples.

But the passage last week of the state's Marriage Equality Act also opens up a host of complications, brought on by differences between New York's law and both federal law and those of other states, most of which don't recognize same-sex marriage.

Uncertainty surrounds matters ranging from taxes to Social Security to divorce and custody, say lawyers who specialize in matrimony and related issues.