Rovio is releasing Angry Birds to 800 million Facebook accounts. Angry Birds Facebook version will be worldwide available on Valentine’s Day (Tuesday, February 14, 2012). Launch event will be held at Jakarta (Indonesia), the second-largest Facebook market after the U.S.

Check out the Official Event page: Angry Birds coming to Facebook!

According to Peter Vesterbacka and Henri Holm from Rovio, Angry Birds Facebook version:
  - will be upgrading to a full screen display
  - higher quality animation
  - include Facebook Leaderboards (more competitive and up to date)
  - introduce new power-ups (such as: special, bigger, or stronger birds) which one can earn while playing the game or buy for $0.99.

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Sources:
i) Penn Olson, Asia technology blog
http://www.penn-olson.com/2012/01/25/angry-birds-facebook-jakarta/

ii) Angry Birds Facebook
http://www.facebook.com/angrybirds