First came the email ghostwriter. Then Oprah and Saturday Night Live and a new mansion. Now Mark Zuckerberg has moved up to the next celebrity accessory, his own security guard.

Mark Zuckerberg and Priscilla Chan get all the press, but they're hardly Silicon Valley's only pair with ten figures between them. Dropbox's twentysomething CEO Drew Houston just became a billionaire — and we hear he didn't reach that milestone alone.

The problem with lists like BusinessWeek's collection of 13 under-30 entrepreneurs: Inevitably, in an effort to fill a demographic quota, editors scrape the bottom of the barrel. And presenting a balanced picture of these business novices cuts against the goal of serving up fresh faces. (Whether they're supposed to…