It seems that privacy questions about social-networking sites are the new black. This time, some customers are expressing concern about LinkedIn, the job-networking site that had its IPO last month.

At issue, a two-month-old site tweak that can turn members from ordinary career networkers into brand cheerleaders with their profile photo and name popping up in related advertising. LinkedIn's privacy policy describes how this could happen: "This advertising may include the fact that you have recommended or endorsed a product...