Sheldon's father's name is George.
When running away from Penny (Kaley Cuoco) and Leonard (Johnny Galecki) arguing, Sheldon (Jim Parsons) rings Howard (Simon Helberg)'s doorbell. This is one of the few times in the entire series that he calls someone to the door without his ritual of knocking and repeating the name three times.
The actor who appears at the end as Penny's guitarist friend, who is crashed out on the couch in Leonard and Sheldon's apartment, is not credited in the episode.
The title refers to Penny's friend who plays the guitar and wants to sleep on her couch to the objections of Leonard, her boyfriend.
Sheldon mentions that Penny moved in three years ago, However, since this episode takes place in 2009, That would mean she moved in the apartment during 2006. It has actually been two years since Penny moved in during Pilot (2007), which was on September 24th 2007, as mentioned in The Focus Attenuation (2014).