Even if you snagged the much touted Angry Birds game "secret code" from the Rio movie ad aired during the SuperBowl, you probably don't know what to do with it. It appears to be a cross promotion due to the Rio-branded version of Angry Birds due as a movie tie-in.
Basically, you need to go to Level 13-12 (if you have it unlocked) and then follow the walkthrough steps in the video below from angrybirdsnest.com to hit a secret spot to reveal a hidden golden egg.
No one seems to be clear on whether this works on all versions of the game or just the iPhone. (Alas, we only have the iPad version and haven't even unlocked that deep into the game yet.) The good news is that this doesn't seem to be a limited time offer, just an Easter Egg that will be there whenever you're ready for it...
Haha that's awesome, though its hard for me to understand how angry birds is so popular. Not really fun in my opinion.