This update includes:
- A new theme in the Frontier Badlands
- 15 new levels and one new golden egg
- Game Center support
- Introduces the Mighty Eagle
My kids have been watching the trailer for the Mighty Eagle for weeks now and can't wait for this update.
For current owners, this is a free update. If you haven't yet gotten in to an avian flinging addiction yet, you can purchase Angry Birds HD from the iTunes Store (link) for $4.99.