1) You can hide that you're online. Just click on the chat icon at the corner of the screen and click the option that says "go offline."
2) You can download your entire Facebook history. Simply go to the Account Settings page; click "Download a copy of your Facebook Data"; and download your entire Facebook history.
3) You can schedule a Facebook status. Going out for a few hours? Flying? Going to be out of the country for an undisclosed amount of time? Not to worry, you can schedule a Facebook status update for those times when you just can't be at your computer, but need to let the world know you still exist.
4) You can edit already published comments.. Simply roll over the comment, click on the pencil icon, and edit away!
5) Get mail you've missed. When you go into your mailbox, check the icon marked "Other". You may have missed messages.