We use the login to auth, seed display name, and for the unique Facebook ID that we only store hashed. There's no analytics of any kind on the site, and except for the display name (which I'm planning on making editable) there's nothing to identify a user if somebody gets access to the database.
One of the things we want to achieve with the service, is to make it hard or very inconvenient to peek at what's been checked off in your own wishlist, and therefore we only use 1 service for login.
It was and still is a really difficult compromise between simplicity, the functionality of the service, and the privacy of our users - which includes my entire family, SO, SO's family, several friends, and many others.
Having reached 200+ users as well, I'm not really sure how we'd go about replacing it with something else as well.