Thanks to xtremesaints for the wording. As usual, all input welcomed.
What is a Shared Journal? How do they work? How Do I create one? (title needs sorting/shortening!)
A shared journal operates in the same manner as a community. For information on how communities work, see http://www.livejournal.com/support/faqbrowse.bml?faqid=77. There are two main differences between shared journals and communities.
Firstly, the Personal Information section of the shared journal will not have instructions on how to join and leave the community like a normal community. Instead, it will display the same Personal Information section as a personal journal.
Another difference between shared journals and communities is that posts are arranged in the order they are posted in a community. If you backdate your entry, the only effect would be to remove it from the friends view of the users watching the community. Shared journals allow you to backdate your entries to arrange their display order by date/time on the entry.
Also, note that shared journals do not appear on the Community Management page (http://www.livejournal.com/community/manage.bml). To grant and remove posting access, you must use the Admin Console (http://www.livejournal.com/admin/console/).
Posting in a shared journal is done in the same way as posting in a community (http://www.livejournal.com/support/faqbrowse.bml?faqid=76).
To create a shared journal, you will need to first convert an existing journal into a community (http://www.livejournal.com/support/faqbrowse.bml?faqid=78). Note that two LiveJournal accounts are necessary in order to create a shared journal. A maintainer account, and the account to be used as the shared journal.
After you have converted the account into a community, you will need to login as the community account (http://www.livejournal.com/login.bml), and execute the following command at the admin console (http://www.livejournal.com/admin/console/).
change_journal_type <examplecomm> shared
where you have to replace <examplecomm> with the community name. Do not enter the < or > symbols; these are only for reference purposes.
To grant users access to the shared journal's Friends Only entries, login (http://www.livejournal.com/login.bml) as the shared journal account, and edit its friends list (http://www.livejournal.com/support/faqbrowse.bml?faqid=61).
To grant posting access to the shared journal, login (http://www.livejournal.com/login.bml) as the maintainer account, and execute the following command at the admin console (http://www.livejournal.com/admin/console/).
shared <sharedjournal> <action> <user>
Do not enter the < or > symbols; these are only for reference purposes. Replace with the name of the journal. Replace <action> with either "add" or "remove". <user> is the username to be added/removed from the shared journal's posting access list.
To convert the shared journal back into a personal account, you will need to first convert the shared journal into a community (http://www.livejournal.com/support/faqbrowse.bml?faqid=78), and then convert it into a personal journal (http://www.livejournal.com/support/faqbrowse.bml?faqid=93)