As an open social network I want to show all profile walls to logged out users. Some of my profiles show activity to unauth. users and some don't:

It may depend on the visibility of the individual journal items. The Default Journal Entry Security setting on the journal page of the control panel can control this.

Thanks Ben. For Default Journal Entry Security Options I have Everyone selected on the Left, and Community Members, Everyone, Friends Only, Group Members and Private on the right?

If you are logged in as the second user, and you hover over the little lock icon next to a journal item, what does it say the permission is?

When I hover over it it says nothing (in IE or Chrome) - when I click on it it says "Community, Everyone, Only Friends and Private".

However, some of the posts on this users wall were made by other users, but no one can see them.

This includes all the "x is now friends with y","x posted an update" etc. - these are what I want public.