Possible privacy settings for quotebooks:
1. Public
2. Public, but not indexable by search engines.
3. Only visible to logged-in users.
4. Only visible to members.
These settings would apply to all quotes in the quotebook. Logged-in users would still be able to get to the quotebook page if they have a link, and perhaps see the quotes there, but probably not on user’s pages unless they are a member of the quotebook (or logged in, in that case). Quotebooks would not show up in the list of all.

There is also the question of who is allowed to edit the quotebook’s settings. Any member?

Similar settings could be made available to users, for their quotes. Quotes of these users would be hidden everywhere that the current user does not have permission to view them.

This could pose problems for pagination. It would be necessary to filter on these privacy settings when the quotes are fetched, not when they are displayed.

Or, controls could be per quote. This would be easier to apply and give finer-grained control, but more difficult for users to change.