Jay Baer says he's changed his mind about Facebook advertising. Despite naysayers, Baer (on his Convince & Convert blog site) now says he believes there's plenty of opportunity in Facebook advertising. First, advertising on Facebook is still an immature field, just 3 years old. Second, the history of self-serve digital advertising, as exemplified by Google AdWords, means that Facebook's model is based on a great one. Even with a nascent advertising system, he says, Facebook will do almost $2.5 billion in advertising this year, and Baer believes it's easy to see why.