Just because your teens aren’t hanging out at the mall, don’t presume they can’t run up your credit card bill. In fact, it may very well be that they are part of the population of online virtual worlds racking up a whopping — dare I say mind-blowing? — 7 billion dollars in sales of virtual goods in 2010 alone. Yes, you read that right — in the midst of a huge economic crisis, people have spent 7 billion (with a “B”) dollars on stuff that isn’t even real.