2012 looks like a great vintage, but ...

The weather has been near ideal so far (fingers crossed for the later ripening reds). Not too hot and not too cool like the last few years. What could go wrong besides some autumn rain?

When the grapes ripen like they do this year there's a danger from some fruit coming in overripe. That is, it didn't get picked at the ideal time. This can happen with heat spikes. That hasn't been a problem yet this year, but a potential labor shortage can be a problem. The grape pickers are almost always Hispanic laborers, usually legal workers, but probably sometimes not. With the anti-immigration feelings, tighter border control, and the poor economy in the U.S. there has been a dwindling supply of immigrant workers. 

Grape picking at night while the fruit is cool

If there aren't enough pickers to go around when the grapes get ripe then some will sit on the vines too long. They will be past their ideal ripeness when finally harvested.  As the grapes ripen sugar levels rise (as will alcohol levels after fermentation) and acids fall. So you may be left with alcoholic, soft, flabby, uninteresting wines in some cases.

The ideal situation to try to prevent this would be a slightly cooler, dry autumn so things can ripen slowly. Or maybe a better idea is to allow, even encourage, the laborers to come. The labor problem isn't just affecting the grape business, but all agriculture.