I think Judge Stephen Reinhardt enjoyed himself writing this opinion, given the way he (subtly) sticks it to the Prop 8 supporters:
1. "[M]arriage is the name that society gives to the relationship that matters most between two adults. A rose by any other name may smell as sweet, but to the couple desiring to enter into a committed lifelong relationship, a marriage by the name 'registered domestic partnership' does not."
2. "We are regularly given forms to complete that ask us whether we are 'single' or 'married.' Newspapers run announcements of births, deaths, and marriages. We are excited to see someone ask, 'Will you marry me?', whether on bended knee in a restaurant or in text splashed across a stadium Jumbotron. Certainly it would not have the same effect to see 'Will you enter into a registered domestic partnership with me?'. Groucho Marx's one-liner, 'Marriage is a wonderful institution…but who wants to live in an institution?' would lack its punch if the word 'marriage' were replaced with the alternative phrase. So too with Shakespeare's 'A young man married a man that's marr'd,' Lincoln's 'Marriage is neither heaven nor hell, it is simply purgatory,' and Sinatra's 'A man doesn't know what happiness is until he's married. By then it's too late.'"
3. "Had Marilyn Monroe's film been called How to Register a Domestic Partnership with a Millionaire, it would not have conveyed the same meaning as did her famous movie."
4. "In order to explain how rescinding access to the designation of 'marriage' is rationally related to the State's interest in responsible procreation, Proponents would have had to argue that opposite-sex couples were more likely to procreate accidentally or irresponsibly when same-sex couples were allowed access to the designation of 'marriage.' We are aware of no basis on which this argument would even be conceivably plausible."
5. "There is a limited sense in which the extension of the designation 'marriage' to same-sex partnerships might alter the content of the lessons that schools choose to teach. Schools teach about the world as it is; when the world changes, lessons change. A shift in the State's marriage law may therefore affect the content of classroom instruction just as would the election of a new governor, the discovery of a new chemical element, or the adoption of a new law permitting no-fault divorce: students learn about these as empirical facts of the world around them. But to protest the teaching of these facts is little different from protesting their very existence; it is like opposing the election of a particular governor on the ground that students would learn about his holding office."