Facebook is working to address a new privacy issue even as this story is being typed.
Early today, mid-afternoon in the UK and while much of the rest of the world was asleep, a story got onto the TechCrunch blog about a new bug. It seems that the chat function, which uses the privacy settings, enabled onlookers not only to see whether you were online, but to observe any other chats you were having and who had applied to friend you.
This is of course crazy. Facebook, to its credit, took the chat function down and it could well be that by the time you read this it'll be back up there with its usual reliability duly restored.