A major reason why the proposition failed wasn't entirely due to "oh crap weed is legal now and everyone will abuse it".
From what I've gathered, it was a few things:
1. Drug dealers and Medical dispensaries started saying no to prop 19 when they thought that it would cut into their profit margins (not all dispensaries thought this, but most drug dealers I've talked with held this view). Counties like Humboldt thought it would utterly destroy their economy, which is why there was a 60+% that voted against 19 in that region alone.
2. Many people did not like the way 19 was written, specifically because some people were not able to find concrete definitions against what people could and could not do in regards to the work place 9transportation specifically). I suggest checking out ballotpedia.com for a good summary of the what's and why's.
3. Because there exist laws in California that keep legislators from altering ballot measures, if prop 19 passed, then it would be very hard to amend the damned text to the law. Meaning if there was a serious problem that was found to exist in the text, it would stay a problem for a good chunk of time (and since their was an uproar about it being possible for transit workers or public transportation workers capable of being high on the job, this became an even larger issue for most people's choices).
I knew it was going to be close, but I was not expecting the near ten point gap that existed when the votes were accounted. I'm actually still unsure if all the provisional and absentee ballots have been accounted for... (not sure how long that typically takes). Hopefully they will rewrite everything for 2012. Swharzeneggersrr may have turned possession into an infraction, but that is hardly a substitute for a well implemented law that legalizes cannabis.
Frankly, I think they should have cloned the already existing regulations for tobacco and alcohol, and tweaked them to fit cannabis better.