Have you noticed anything different about Facebook? Yesterday when I was checking out my profile, a new chat pop up appeared showing me all of my groups of friends. I didn't think much of it and then I realized — new filter functionality in chat — yippee! Facebook has already improved friend organization with their Friends list feature, and now you can control which groups of friends see you online.
Now you can check off certain lists you want to include in the chat pane so you can be online and chat with close friends, and your work colleagues won't know you're available to chat. You can also create new lists by selecting the "Friend Lists" menu on the Chat pane, then enter the name, and drag whoever you want to be included in that list. And if you don't want to appear online to anyone, you can turn off the green switch beside a particular Friend list (they will not be able to see if you are online), or just choose Options and go offline altogether.