Facebook, being the largest site on the planet and not content with that, is always testing new features and changes, to the despair of most of its users.
But while the users moan and complain, they don't go anywhere and most of the time, the changes are for the best, people just don't like to change all that much.
One of the most recent tests is a reply button in the comments section, for status updates. What this does is enable users to reply to a specific comment rather than just add their comment to the rest of them.
It should make it easier to follow a conversation, especially when there are more of them going on in a comment thread. It is possible to reply, in a way, to specific comments by adding an @reply to your comment.
Facebook is also testing audible notifications which would ensure that you don't miss any notification as it comes in.