I love these two screenshots from Sparrow's new iPhone app because they confirm a few threads that I routinely discuss / think about. The screenshots appear after app download and after your mail account is connected - you are prompted of course to connect the mail account with Facebook ("mail is much nicer with your friends' profile pictures!"): 1. First and foremost, Facebook should be considered an identity platform as much as it is a considered a social network. I firmly believe this.
2. Outsource to Facebook (and other major platforms) in areas where they do things better (ie identity, sharing) or where you gain advantage elsewhere (ie Facebook Connect + mail account = superior data / future functionalities).
3. Mail still needs to be rethought and Sparrow gives it an interesting twist.
4. Facebook should play a bigger role in email 2.0.