In order to make sure each area has great content, recent public posts are analyzed electronically and then placed into the areas where they best fit, if there is indeed such an area. (Not all entries will necessarily appear in an explore area.) [...] First of all, let us reassure you that the only entries that will ever appear in the explore areas are public entries. However, you will have a few options if you don't want a post of yours to be included in the explore areas. You can remove individual posts that are currently appearing in an explore area by clicking on the delete button next to that entry. This will not delete your entry from your journal; it will only remove it from appearing in that explore area. If you want all of your public entries to be excluded from the explore areas, you may opt-out by going to Viewing Options and checking the box labeled "Explore Area Exclusion." Journal entries posted as private or friends-only are automatically excluded, but this will also exclude your public entries from the explore area.I'm not a fan of opt-out schemes, myself -- particularly when they're implemented in a way that isn't apparent to users who are not in the habit of checking for change announcements. They're changing the default ruleset. As far as I can tell, there isn't even a way to set a given entry not to publish within the "post" page; if I'm right, you have to wait for it to publish and then retract it. I suspect the same is true for people who use other methods (clients, IM, text messaging, etc.) to post.
So if you generally leave your posts public, you should know that LJ will now aggregate and publish them, and you should consider whether you want to turn that ability off in your journal.
(N.B.: The title is a shout-out to gnomi, who has likened posting online to shouting in the public square -- except that posting stays out there forever.)