Today, the 1st Circuit Court of Appeals in Boston ruled that DOMA is unconstitutional. The law, which prohibits same-sex couples from accessing many of the benefits that heterosexual couples receive, has been debated heavily for years, but this is the first major ruling to strike it down since 2010. While the ruling will likely be appealed to the next highest court, it still give marriage-equality advocates reason to celebrate.
The argument from those who support the ruling is that it is up to states to decide what constitutes marriage and who should get those benefits. While many states have banned gay marriage, eight have so far made it legal. In those states, and others where such marriages are recognized, legally married couples were being denied certain things that the federal government offers to straight couples, such as survivor's benefits, jointly-filed taxes, and medical benefits.
Those who oppose the ruling do so on the grounds that same-sex marriage itself is wrong, and that granting these couples that they feel are married wrongly these benefits constitutes a weakening of traditional marriage. They claim that, by offering these benefits, the government will encourage more people to engage in same-sex marriages, and that there could be rampant fraud as a result (never mind that marriage fraud may already be a problem among heterosexuals - I haven't seen any reports on it).
Personally, I feel this is a huge step forward for America. It means that people are no longer treated like second-class citizens because of who they are. We're all Americans, and we should be treated as such.