Did the actor do all his own Singing?
The actor playing Conor's voice was pretty shaky and off when rehearsing, but he sounded really good when performing. Did he actually sing all the songs?
Unrelated observation: in the songs at the school dance, he looked and sounded a lot like Green Day's Billie Joe Armstrong.
Unrelated observation 2: the actor playing older brother Brendan looked like Seth Rogen in the movie.
Great movie.
edit: I went back and watched the credits, I guess the actor did sing all the songs. Kudos to him.