Obviously, the next two days are going to be important ones in establishing the parameters of gay (and straight) rights in this country (http://www.politico.com/story/2013/03/can-gay-marriage-survive-a-scotus-loss-89304.html?hp=t1).
For conservatives who support gay rights, including the right of gays to marry, there are some tricky questions. Do societies have the right to legislate about sexual mores? That's one of the big issues at stake. If the Court strikes down Prop. 8, it's hard to see how anyone can ever argue again that the state (i.e., citizens as a group) has any interest in regulating any kind of sexual behavior between consenting adults, regardless of whether that behavior may have deleterious effects on family stability or the welfare of children. (That's not to say that gay marriage will necessarily have these effects; the point is that we don't know - but striking down the law is an implicit statement that such rationales do not pass constitutional muster).
it's also hard to see how conservatives can cheer on the prospect of the Supremes finding a right to gay marriage in the Constitution and then consistently argue against the jurisprudence of cases like Roe vs. Wade -- or call themselves strict constructionists.
On the other hand, there is some inconsistency on the part of the lefties who favor overturning both Prop. 8 and DOMA. How does one insist, on the first day of arguments, that the people of California had no right to define marriage as between a man and a woman -- and then, on the second day, argue that DOMA should be struck down because it does not respect the right of states that have chosen to recognize gay marriage? Either states have rights to define marriage for themselves, or they don't.
To me, it seems that gay marriage is the kind of question best reserved for state legislatures, rather than for the Court to find a wholly new, hitherto undiscovered (and, a decade ago, wholly unimaginable) "right" to gay marriage. The latter is the course it chose in Roe, thereby spurring decades of bitter politics, rather than allowing the people themselves to make their voices heard and then to decide. Are there practical difficulties in such a course? Absolutely -- but anyone who hates the division and bitterness of America's abortion politics can understand why it's better to let elected state (and federal) legislatures (and/or their citizens), rather than unelected and unaccountable judges, make these kinds of decisions.