Today's 4-3 decision of the California Supreme Court striking down under the California Constitution a California statute limiting "marriage" to opposite-sex couples could help John McCain in the fall. (More coverage of the opinion itself at How Appealing.) The decision is based upon the California Constitution, which can be changed by the voters. And, according to this story in the S.F. Chronicle, it seems very likely an initiative overturning the decision through a constitutional amendment will qualify and appear on the November ballot.
This helps John McCain because those conservative voters may not have come out in great numbers for him, but they will come out now to vote for this amendment, and they are more likely to vote for McCain than for the Democrat once they are already voting. That's not to say that California will go red, but it is to say that the Democratic nominee will have to devote more resources to this very expensive to campaign in state.