As you've probably already read through other sources, Obama made a very hasty announcement recently that he supports gay marriage; this is being seen as a marker of a cultural shift in the United States, and rightly so. It's still a divisive topic, but the polls are encouraging that while there are still enormous regional differences, popular support for gay marriage is growing, and that the way it is growing is through a strong generational divide; the changes are likely to be quite permanent.
What you might not have caught was the mess that led to the haste of this announcement; Obama's public line has been that his views are evolving on the topic, but in his recent announcement interview, he noted that he actually had reached his position last September and was looking for a more opportune time to announce it; Joe Biden's surprise announcement that he (Biden) personally supports it in a recent interview made Obama's continued silence untenable, leading to a need to unveil it immediately (and a chiding of Biden that no doubt has been more direct behind closed doors).
If you want to see some amusing squirming by Carney (Obama's press secretary), check out this press conference, particularly 22:30-23:30. (Yes, I catch most of these press conferences).
It's probably forgivable that Obama would not announce his positions immediately when he reaches them; there would be little utility in announcing a position that isn't very stable, particularly on a contentious matter like this. It does feel a bit weird that he'd let a stable position sit this long without being willing to admit it, but that level of deception is well within the bounds of what we expect of our politicians, for better or worse.
From my perspective though, while this is a marker of societal change, it's not a genuine achievement; Obama may be a powerful figure in our government, but he doesn't have the ability to make gay marriage legal on his own; it would (ideally) take a Supreme Court decision that it is implied by equal protection (making it legal throughout the entire United States in one go, and the right way to do it in my opinion) or various kinds of legislature.
The Republican party is playing a losing game in the long run by remaining opposed to gay marriage; given the evolving demographic, having taken a firm stand against civil rights will be something future Republicans will resent needing to acknowledge in the history of their party.