The Facebook Divorce Announcement

Have now had an old friend and a neighbor recently announce their divorce to the world by changing their Facebook status from married to single. It's a disturbing reminder that relationships are fluid and temporary. It also raises etiquette questions. Are you supposed to comment on the status notification? Next time you see them in person, are you supposed to ask or should you pretend like you didn't notice and wait for them to bring it up? I'm taking the latter approach because there is less potential for disaster.