Back in the day, professionals used to keep their business separate from their social lives. That's not the case anymore. In fact, with Trulia's new Facebook Connect feature, real estate professionals no longer have to make any distinction between their professional versus not-professional networks. Beginning Friday, real estate agents and brokers signed up with Trulia can link their online portfolios to Facebook and "expand their footprint and drive more inquiries" to their business. How great — two social networking sites, buddy-buddy to bring more business to both of them. The agreement does raise a few questions, though. After all, Facebook doesn't need the extra marketing, -- what with 500 million members, and a CEO who is the zeitgeist du jour and Time's Person of the Year. But, I guess synergy can never go too far. That is, unless Facebook becomes too big to fail. Write to Christine Ricciardi. Follow her on Twitter @HWnewbieCR.