Don’t forget about user engagement. That’s the basic lesson of the Facebook app WSJ Social that The Wall Street Journal has just unveiled.If your business Model is a paywall site, your general approach is drive as much traffic as possible to the site and begin the conversion process – through free emails, trials, etc. The WSJ move is reminding us that engagement is important too, even if it takes place off the main site.But will engagement convert more subscribers? Time will tell.”We’re breaking the mold of using Facebook simply to drive traffic to our websites and are now creating an opportunity to engage with the Journal directly on the Facebook platform,” said Alisa Bowen, the WSJ Digital Network’s GM said in a statement. “WSJ Social creates a more integrated experience for users and innovative opportunities for advertisers.”The app is launching based on a sponsorship Model. Dell is sponsoring app user access paid content for the first month. Other companies may follow suit, providing either a nice revenue stream for the WSJ or a bit of cannibalization of its paid subs or a bit of both.