I don't know how many times I will have to say it but, again, Sheldon and Penny's interactions are what make this show good. Wolowitz and Koothrappali might as well not be there for the amount of entertainment they give. I especially like the start of this episode where Sheldon asks Penny not to need to have sex with Leonard. Laugh out loud funny.
Sheldon's OCD about knocking three times came to light today, again adding an extra annoying and funny characteristic to Sheldon.
However, I did find Sheldon slightly annoying this episode due to his interference in Leanord's love life. I don't know if its due to the fact that I like the actress Sara Rue, who plays Leonard's current girlfriend, but I really want it to work between them two and can see Sheldon's constant 'helping' to be a hindrance.
As i said last week, a step in the right direction towards this show loosing its failures at the start if this series and hopefully this will stay until the end of the series.