I'm not suggesting you duplicate the feature set that Facebook provides. If a user wants to have those features, it makes sense to have them link their Facebook

I'm not suggesting you duplicate the feature set that Facebook provides. If a user wants to have those features, it makes sense to have them link their Facebook account. But I would probably offer a more basic version that doesn't have friend lists, SMS reminders, etc, and let the user opt in to the additional features only if they wanted to. Otherwise I think you might end up artificially restricting the amount/type of users that use your site (e.g. people without Facebook accounts or people that want to keep their Facebook data private).