Kevin Drum is optimistic:
I know this won't be much solace to everyone who worked on Prop 19, but.....this isn't so bad, really. Given the automatic headwind of getting people to vote Yes on anything, the additional headwind of a big Republican turnout, plus the general nervousness that middle class people have about drugs, a loss this small is actually sort of encouraging. All we need to turn this around in a few years is for 4% of voters to change their minds.
What's more, the threat of Prop 19 passing probably helped to get the penalty for pot possession reduced from a misdemeanor to an infraction. So now, on the off chance that you get caught with a small bag of weed, all you get is the equivalent of a traffic ticket. A lot of people think this reduced the incentive to vote for Prop 19 and thus helped to defeat it, and maybe it did (though I'm skeptical). But it still means we made progress. And we're not very far from making even more. Probably not in 2012, but I wouldn't be surprised if something similar to Prop 19 could pass by 2014 if the stars align favorably.