At some point over the next few weeks, you’ll get a notice on your Facebook page telling you Timeline is enabled. You have seven days to clean up your profile and customise Timeline to your liking before the rest of your friends see it. This is a good time to take a look at our guide to hiding embarrassing old posts to make sure you’re not broadcasting anything you don’t want to. If you don’t feel like waiting until Facebook automatically updates it for you, you can still opt-in and enable it right now.
Timeline:Now Available Worldwide [Facebook Blog]