Ah, a social media business that works. LinkedIn reported a strong Q4, with revenue doubling to $168 million and net income of nearly $7 million. That, and positive guidance, raised shares after hours. The professional social network saw better growth in the services it sells surrounding recruiting, but advertising was up 77 percent. LinkedIn said it has 150 million members, and 15 percent of visits came from mobile devices. It made some vague comments about offering mobile advertising at some point. Fifty percent of LinkedIn’s revenues come from what it calls hiring solutions, and a good deal of its premium subscriptions business revolves around jobs as well. Be sure to tune in to a GigaOM Pro webinar on The New Recruiting Ecosystem on February 15.