This shift roughly follows the same trend found by Gallup among all Americans, although not exactly. Looking at the same time frame (2006, 2009, 2012), there was slightly more support among all Americans compared to Latinos for gay marriage in 2006, but now in 2012 there is significantly more support for gay marriage among Latinos.
The issue of same-sex marriage sharply divides the American public along political and religious lines. Almost two-thirds of Democrats support legalizing it, compared with 57% of independents and 22% of Republicans.
Also, Gallup explained that in 2011, the increase in support for gay marriage came exclusively from Democrats and Independents, while Republican support remained flat. Assuming that that is, for the most part, a consistent trend in recent years, it suggests that Latinos became more supportive of gay marriage along with their fellow Democrats, rather than because of a Latino-specific trend, just based on the numbers.
Oh, and if anyone here is interested in the Presidential race, the numbers are quite strong (the data is from mid-September, but was just released yesterday) for President Obama as well, in line with what other surveys of Hispanics have found:
Mitt Romney's Latino Support Fueled by Evangelicals
PS-Please check out my new book Obama's America: A Transformative Vision of Our National Identity, published last month by Potomac Books. You can read a review by DailyKos's own Greg Dworkin here.