GM sold about 30,000 Volts and Opel Amperas (basically a rebadged Volt) in 2012, and according to what anonymous sources "who didn’t want to be identified because the target isn’t public" told the Washington Post, the company is planning to increase that number by about 20% to 36,000 in 2013.
Chief Executive Officer Dan Akerson has struggled to compete against more successful alternative-power vehicles such as Toyota Motor Corp.’s Prius. The CEO originally touted the Volt’s gasoline-and-electric system as the technology of the future and forecast global Volt sales of 60,000 in 2012, before settling for half that amount.(source)
I've written more about plug-in sales and sales targets here: Are plug-in cars selling badly?
While GM management might find it frustrating that sales are hard to predict and the global economy won't seem to pick up steam and help them achieve a higher run-rate, Volt owners seem pretty pleased: "The Volt, chosen as 2011’s North American Car of the Year, succeeded in satisfying its customers, with 92 percent of survey respondents telling Consumer Reports they would buy one again -- the second straight year it ranked highest."
One thing's for certain, the more Volts (and plug-in in general) any company makes, the better they can spread their fixed costs over a larger number of units, which should over time result in cheaper plug-ins. We've already started to see this with the Nissan LEAF, for example.