LJ etiquette

Dear Ms Manners[0],

How long is a post allowed to be before I lj-cut it. theferrett says that you should never use them (See tip #6). What do you think?

When you inadvertantly post a comment anonymously, is it best to let the comment go or to post an annoying followup "Oops! I posted this!" message? Or do you rely on the LJ-owner to deduce your life story based on IP address?