It was posted (KinchBlade I think) that the goal is to be able to play the songs in Rocksmith outside the game. While I can play quite a few song riffs now, I'm only now getting where I can play a full Rocksmith song outside of Rocksmith (I have a few others I've learned on my own that I can play).
One problem I have is getting the song started in my head so I can begin playing. I'll get (most recently) Synchronicity II stuck in my head and I won't be able to start, Smoke On The Water for instance. I know the chords but can't get the rhythm started to play the song (or bit of song).
Anyway, my first Rocksmith song that I can play outside of Rocksmith is:
Judas Priest - Breaking The Law