The fact that you can play Angry Birds on basically every device under the sun is pretty cool. What's less cool, however, is that your progress isn't saved between devices. With the newly launched Rovio Accounts, that's something Rovio is hoping to change.
When you create a Rovio Account for a game you're playing, your progress is then associated with that account. So when you sign in on another device, your progress is waiting for you. This isn't exactly new -- we've seen quite a few developers offer a similar feature in the past -- but it's still good to see a studio as big as Rovio adopting it.
For the moment, The Croods and the original Angry Birds are the only games offering Rovio Accounts. The former has been rolled out worldwide, and the latter is currently only available in Finland and Poland. Rovio plans on bringing the service to all of their games in the future, so be on the lookout for that.
In the meantime, have fun playing The Croods, I guess?