The value prop of social sign on
Social authentication is definitely gaining traction, and Fandango makes good use of the value proposition of social sign on - visually presenting the benefit of socializing the web experience.
Make sure to utilize your "About this app" section to reinforce and romance the benefits of connecting with Facebook:
Fandango's Movies With Friends landing page also does a thorough job of communicating how the app works and how it benefits the user.
Socializing the product page
Product reviews are no longer the holy grail of humanizing a product page. Fandango identifies another element of social proof - intent to buy. Site users can indicate "I'm in" or "I'll pass" and share that with their friends.
It's a good idea to create social features that are meaningful even if a Facebooker's friends aren't using the app. Fandango reports both site users' results and Twitter sentiment.
Word of mouth
Timeline apps gain one-time permissions that allow the brand to post updates automatically, so think about ways your customers may already be talking about your content or products offline, and determine how you can bring those into the purchase (and consumption) experience. Though your Timeline app may not be directly transactional, it could be your most powerful word of mouth tool.
Facebook Timeline Apps present a great opportunity for digital disruption. It will be interesting to watch what other brands develop in the coming months.