That being said, as a general FYI: I played with this new LJ feature using a dummy journal and a fake FB account, and it's actually impossible for your flocked posts to show up on someone else's Facebook. When someone who uses this feature comments on a flocked post, their comment shows up on their wall and links to the post in question -- which, like any other link to a flocked post, goes to LJ's "you must be logged in to see this entry" error page. The subject and content of the original post don't appear anywhere on that user's FB wall.
Also, so long as your Facebook isn't connected to your LJ, those creepy little toggle-boxes next to posts and comments can't be clicked. The only way to actually have YOUR journal content show up on Facebook is to activate the LiveJournal application, which is virtually impossible to do on accident.
I hope this assuages other people's worries like it assuaged mine. Make no mistake, this feature is still extremely unwelcome and uncool, but it doesn't look like the average LJ user runs much risk of getting their chocolate in their peanut butter.