On Supreme Court's recent ruling in Christian Legal Society v. Martinez:
Theodore Boutrous, one of the attorneys for the plaintiff side of Perry v. Schwarzanegger just wrote up a letter to Judge Walker that highlights this.
From prop8trialtracker.com (courage campaign website):
In Christian Legal Society, the Supreme Court definitively held that sexual orientation is not merely behavioral, but rather, that gay and lesbian individuals are an identifiable class. Writing for the Court, Justice Ginsburg explained: “Our decisions have declined to distinguish between status and conduct in this context.” Slip op. at 23 (citing Lawrence v. Texas, 539 U.S. 558, 575 (2003); id. at 583 (O’Connor, J., concurring in judgment); Bray v. Alexandria Women’s Health Clinic, 506 U.S. 263, 270 (1993)). This confirms that a majority of the Court now adheres to Justice O’Connor’s view in Lawrence, where she concluded that “the conduct targeted by [the Texas anti-sodomy] law is conduct that is closely correlated with being homosexual” and that, “[u]nder such circumstances, [the] law is targeted at more than conduct” and “is instead directed toward gay persons as a class,” id. at 583 (O’Connor, J., concurring in judgment) (emphasis added). See also Romer v. Evans, 517 U.S. 620 (1996) (treating gay and lesbian individuals as a class for equal protection purposes). The Court’s holding arose in response to Christian Legal Society’s argument that it was not discriminating on the basis of sexual orientation, but rather because gay and lesbian individuals refused to acknowledge that their conduct was morally wrong. The Court rejected that argument, holding that there is no distinction between gay and lesbian individuals and their conduct.http://prop8trialtracker.com/2010/06/29/boutrous-sends-letter-about-yesterdays-scotus-ruling/
Most of the Supreme Court, including Anthony Kennedy, made no comment in Lawrence v. Texas (or any other case) as to whether sexual orientation is an immutable characteristic. This precedent strongly suggests that a higher standard than the rational basis test may be used to make a determination in Perry v. Schwarzanegger.