Marriage Support Tipping Point?

Nate Silver has analyzed the latest polling on support for same sex marriage and finds it 50.5% opposed and 48.5% favor, i.e., too close to call.  He also notes an acceleration in support for marriage equality with a 4 point gain over the past 16 months:

Something to bear in mind is that it's only been fairly recently that gay rights groups -- and other liberals and libertarians -- shifted toward a strategy of explicitly calling for full equity in marriage rights, rather than finding civil unions to be an acceptable compromise. While there is not necessarily zero risk of backlash resulting from things like court decisions -- support for gay marriage slid backward by a couple of points, albeit temporarily, after a Massachusetts' court's ruling in 2003 that same-sex marriage was required by that state's constitution -- it seems that, in general, "having the debate" is helpful to the gay marriage cause, probably because the secular justifications against it are generally quite weak.