Storable Data

From Facebook Developer Wiki

Platform Policies III: Storable Data

You cannot cache any user data you receive from Facebook for more than 24 hours unless doing so is permitted by the offline exception, or that data is explicitly designated below as "storable indefinitely."

However, with respect to the Statement of Rights and Responsibilities clause 9.2.4, if the user de-authorizes, disconnects, or otherwise disassociates from your application, the permission to “store indefinitely” is rescinded for all user data you received from Facebook except for the User ID. In that event you can retain the User ID indefinitely (so that you can recognize the returning user, identify who created Independent Data in your application, or for other purposes limited to use related to your application), but all other user data you received from Facebook must be deleted as soon as possible (and in no case longer than 24 hours after you received it).

Offline exception: Applications that run on a device controlled by and possessed by the user -- such as desktop or laptop computer, mobile device, or other embedded device -- can cache user data received from Facebook for more than 24 hours only when Internet connectivity is unavailable or it is impossible for the application to run. Such data can be stored on the client device but not a remote server, and cannot be made available to the developer. Cached data older than 24 hours can be displayed to the user (or otherwise used by the application) in lieu of updated data only until an update is possible, and in no case beyond 14 days after the last update.

User data you receive from Facebook that you can store indefinitely:

uid	User ID
nid	Primary network ID
eid	Event ID
gid	Group ID
pid	Photo ID
aid	Photo album ID
flid	friend list ID
listing_id	Marketplace listing ID
page_id	Facebook Page ID
proxied_email	Placeholder email addresses for your users
notes_count	Total number of notes written by the user
profile_update_time	Time that the user's profile was last updated

The storable IDs enable you to keep unique identifiers for Facebook elements that correspond to data gathered by your application. For instance, if you collected information about a user's musical tastes, you could associate that data with a user's Facebook uid.

However, note that you cannot store any relations between these IDs, such as whether a user is attending an event. The only exception is the user-to-network relation.