Most big social networks are fun to use but tough to turn into businesses. Facebook struggled mightily before finding its fortune in mobile advertising; Snapchatâs television-like ad business is an open question; Twitter is in turnaround and likely headed for a sale. For a long time the work-centered social network LinkedIn, which was acquired by Microsoft yesterday for $26.2 billion, had the opposite problem: it was a reliable generator of cash, but is disdained by a large swathe of its user base....
