If you are already using the following modules, you can easily make a guestbook or an http://drupal.org/project/facebook_status alternative without additional modules.
http://drupal.org/project/comment_upload if you need photos
1. Create a content type guestbook
2. Make this content type a content profile node
3. Make a mini Panel with user context showing only comments and comment form for this content type
5. Place the mini panel in the user panel and make the setting as Tab - http://drupal.org/project/panels_tabs
4. Make a Redirect Panel http://drupal.org/project/page_manager_redirect which redirects to the users profile when someone
wants to view a node of that type to the coresponding tab e.g. http://www.example.com/user/%author:uid#guestbook
5. activate http://drupal.org/project/comment_upload if you want to attach photos to a comment
The principle is that guestbook entries or facebook statuses are comments.
What do you think?
I am sure there are other ways as well. The good thing with the above approach is that you can do very complex visibility rules within panels using UR relationship, OG, Context ...
Comment form is hidden for anonymous users, but comments are visible.