Prop 8 was meant to codify what was already implicitly in the state constitution (because that was what the people who wrote the constitution assumed) - marriage is between a man and a woman. Because of the state Supreme Court, it ended up being a restoration instead of a mere codification.
I would not call it a "ban on gay marriage". Gays have been "marrying" each other for a few years now, and they are allowed to do that. Prop 8 doesn't bring the force of law down on them. But they should not have the power to force the people of California, against or will, to neuter our marriage licensing.
http://walrus.blogtownhall.com/2009/05/26/handy_dandy_marri age_neutering_plea_repellant.thtml