Go here if you haven't already.
Short version: LJ's instituted a system for marking content and journals as explicit or adult. It's also instituted a method for flagging "inappropriate" content for the Abuse Team to look at--stuff that should be marked adult-only but isn't.
This includes entire journals, y'all.
I'm going to set this journal to Adult in 24 hours, which means that anyone with a journal that was created with a birthdate indicated underaged status won't be able to view my entries. But hey, if I get a whole buncha new people with brand-new of-age journals friending me all of a sudden, I won't say a word about it.