In 2011 and early 2012, support for marriage equality was increasing at a rate of about two percentage points per year, while opposition was decreasing at the same rate, for a change in the margin of about four points per year. Following Obama's statement in support of marriage equality, PPP's state polls show an additional change in the margin of about seven points, a substantial jump equivalent to leaping ahead about two years.
Most surprisingly, an increase was seen in all demographics, including conservatives and Republicans. Honestly, I thought support for gay marriage among Republicans would decrease out of sheer contrariness.
Below, you can see a comparison in the change in margin for pairs of state polls where the second poll was completed either before or after Obama's interview.
There's a lot of fine print, but basically on the left, you can see the change in margin from one poll to the next in the same state, usually about six months apart, under baseline conditions where the margin was improving about two points every six months (four points per year). There's a lot of scatter, as expected for polls of this size. On the right, you can see the change in margin for seven states where PPP has asked about same sex marriage after Obama's interview, compared to a poll completed about six months before the interview. Clearly, the change in margin is much greater when the second interview was completed post-interview.