Both Nate Silver and Ezra Klein see no fallout (and perhaps a tiny boost) in the polls for Obama over his same-sex marriage endorsement.
As it happens, today is the first day that all of the polls included in the Real Clear Politics head-to-head average were taken fully or mostly after May 9th, the day President Obama endorsed gay marriage. As of this morning, they show Obama with a 1.7 percent lead. Looking back at the Wonkbook Dashboards, on the morning of May 9th, however, Obama had a 0.2 percent lead in the RCP head-to-head average. So since coming out for gay marriage, his numbers have slightly improved.
A 1.5 percent swing in the polling average isn't nothing. But it's not much. And it's certainly not clear it was caused by Obama's comments on gay marriage. What we can say is that for all the hubbub, and all the column inches devoted to gaming out the political fallout, Obama's announcement led to little evident movement in the polls, and what movement there has been has been in his favor.