It's always hard to tell about this, but it seems possible that the Ohio amendment banning same-sex marriage brought more religious conservatives to the polls, perhaps enough to make the difference — or at least to contribute substantially to the difference — in the close presidential race there. It's not certain; among other things, some speculate that this may have brought out many black voters who are anti-same-sex-marriage but who vote Democratic.
Still, if it's so, then it suggests that the Goodridge decision, by making people feel that traditional marriage rules are in jeopardy from courts, may have ended up costing (or helping cost) Kerry the election. And the decision may have had a similar effect not just in Ohio, but in other close states in which some voters associated Democrats with likely support for same-sex marriage, and assumed that Kerry appointees would be more likely than Bush appointees to implement Goodridge on the federal level.
Now, as I've blogged before, I'm tentatively in favor of allowing same-sex marriage; I would have voted against the Ohio ballot measure. And of course if one thinks that the Constitution really should be interpreted to ban opposite-sex-only marriage, then one may well support courts' deciding this, come what may. But I think that even supporters of same-sex marriage should recognize the possible political backlash that may come from such decisions being made by judges, based not on text or history, but on a moral argument (about the constitutional equality of same-sex and opposite-sex marriage) that faces broad, nationwide opposition.
UPDATE: John Fund in OpinionJournal's Political Diary takes a similar value. Likewise, my student Sean Hayes, whose parents are from Ohio, says that the anti-same-sex-marriage initiative was indeed a big issue there, and he thinks it could have indeed swayed 130,000 votes, and another reader makes the same point. Impossible to tell for sure, of course — but it does seem like this election might indeed have turned on the anti-Goodridge backlash.