William Eskridge Jr. wrote CASE FOR SAME SEX MARRIAGE: From Sexual Liberty to Civilized Commitment in 1996 and it has held up well over time. See, e.g., Same-Sex Marriage: The Legal and Psychological Evolution in America, by Donald Cantor et. al., which looks at it from various angles, including how marriage overall has developed in recent years. Thus, we are left with NY being the only state to my knowledge without a true "no fault" divorce law,* though first cousins (yeah Darwins!) could marry there. This development changed marriage writ large in ways much greater than same sex unions has where they all state sanctioned.
The case will go next to the U.S. Court of Appeals for the 9th Circuit. And if the voters don't moot it by repealing Proposition 8 in 2012, the last stop will probably be the Supreme Court.
If the appellate court upholds Prop 8, it is somewhat unlikely that the SC will accept the case. It very well might be possible that even if they strike it down that the SC will not take the case. This would include how the ruling is written.
After all, California already has a statewide domestic partnership law which protects most of the privileges of marriage. Thus, the "state interest" in having Prop 8 is weaker than some other state (including those in the Ninth Circuit) without that. The state legislature was open to a same sex marriage law and the CA SC held it was required under the state constitution. The possible "animus" of Prop 8, as compared to existing laws elsewhere provides a narrow construction.
And, the Supreme Court left in place preliminary protections of marriage rights and homosexuals in the past. The CA Supreme Court was twenty years ahead of Loving v. Virgina, resting on federal constitutional grounds:
Since the right to marry is the right to join in marriage with the person of one's choice, a statute that prohibits an individual from marrying a member of a race other than his own restricts the scope of his choice and thereby restricts his right to marry. It must therefore be determined whether the state can restrict that right on the basis of race alone without violating the equal protection of the laws clause of the United States Constitution.
Particularly if it rests on narrow grounds, which would probably be advisable (the ruling need not block further protections, just as narrow early free speech rulings left an opening for broader protections), the Supreme Court could feel it advisable to let things simmer before taking the case. Did it take a case when the lower court upheld an outlier law that completely banned same sex adoption?
OTOH, recent events suggest this is not something to rely too much on.
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* As the link suggests, NY's practices is troublesome in part because it is out of step "with modern views of marriage," which in effect burdens the basic right at stake.
Refusal of the NY Senate to pass a same sex marriage law [though out of state same sex couples, including those from Connecticut, are recognized ... notably out of state "civil unions" are not] is therefore not the only "right to marriage" issue the state needs to address.