For what it’s worth, many courts would have upheld Proposition 8:

New York Court of Appeals? Upheld in New York:  

The majority decision, written by Judge Robert S. Smith, who was appointed by Gov. George Pataki, found that limiting marriage to opposite-sex couples could be based on rational social goals, primarily the protection and welfare of children. “Plaintiffs have not persuaded us that this long-accepted restriction is a wholly irrational one, based solely on ignorance and prejudice against homosexuals,” Judge Smith wrote in his 22-page opinion. For example, he wrote, it could be argued that children benefit from being raised by two natural parents, a mother and a father, rather than by gay or lesbian couples.

US 8th Circuit Appeals Court? Upheld in Nebraska:  

Loken noted “historical fact – the institution of marriage has always been in our federal system, the predominant concern of state government. … This necessarily includes the power to classify those persons who may validly marry.” Citing the recent decision of the New York Court of Appeals, the circuit court found two justifications for Nebraska’s marriage law. First, it noted that the state had a legitimate interest in inducing opposite-sex couples, who could unintentionally bear children, into stable relationships. Second, the state could base its law on the traditional notion that children do best when raised by two parents of the opposite sex. The court found that both these interests were rationally related to Nebraska’s constitutional amendment. The court also rejected the plaintiffs’ claim that this case was controlled by the U.S. Supreme Court decision in Romer v. Evans. Romer involved a state constitutional amendment that invalidated certain local ordinances prohibiting discrimination on the basis of sexual orientation. The Romer Court held that the amendment was not rationally related to a legitimate state interest, but was clearly the result of “animus.” 

Maryland Court of Appeals? Upheld in Maryland:

In an opinion signed by four judges, Judge Glenn T. Harrell Jr., citing a Supreme Court holding on judicial restraint, wrote that, absent evidence of discrimination, “judicial intervention is generally unwarranted no matter how unwisely we may think a political branch has acted. In declaring that the State’s legitimate interests in fostering procreation and encouraging the traditional family structures in which children are born are related reasonably to the means employed by [the law banning same-sex marriage], our opinion should by no means be read to imply that the General Assembly may not grant and recognize for homosexual persons civil unions or the reasons,” wrote Harrell, who is retired from the court but participated in the decision because he was a member when the case was argued.

California Supreme Court? Upheld before Walker:

California’s historic 2008 ruling, written by Chief Justice Ronald George, repeatedly invoked the words “respect and dignity” and framed the marriage question as one that deeply affected not just couples but also their children. California has more than 100,000 households headed by gay couples, about a quarter with children, according to 2000 census data.

(For what it’s worth, the LA Times notes that “Gay rights lawyers had no solid legal precedent on their side, and some of the court’s earlier holdings on constitutional revisions mildly undercut their arguments.”)

Washington Supreme Court? Upheld in Washington:

Johnson wrote that the Legislature had “a compelling governmental interest in preserving the institution of marriage, as well as the healthy families and children it promotes. This conclusion may not be changed by mere passage of time or currents of public favor and surely not changed by courts.”

UPDATE: The Institute for Marriage and Public Policy has a new report on this very subject [PDF link].