In answering this request
I realized that I couldn't find a FAQ that pointed out that you can't see protected entries on someone else's friends list (or maybe there is one, and it just isn't in one of the places I thought to look?). I think (hope...) that it's obvious that you can't see protected entries by people who have not friended you, but it's not intuitive to me that you wouldn't see mutual friends' or communities posts.
Would it be appropriate to add a section to http://www.livejournal.com/support/faqbrowse.bml?faqid=219
[what is a friends page] about viewing other users' Friends lists? Possibly add in a mention of friendsfriends as a paid feature there, and note that the same public-post rules apply?
Edited to clarify: the mutual-friend and community viewing wouldn't apply to friendsfriends, but the security part would.
Edited again - it didn't occur to me to look in the troubleshooting category, and it's covered in http://www.livejournal.com/support/faqbrowse.bml?faqid=92
[Why don't journal entries show up where they should?].