I have read before that custom user titles would be only available after posting 500 posts or becoming a premium but I and other people can change the user title without having non of the requirements. Is this supposed to happen?
Jordan tweaked the rules for all registered users, as of last week...No announcement, he just thought you would all enjoy the feature.
With that said, there are some words that are not permitted in user titles (administrator, moderator, owner, banned, et cetera); anything else not permitted by the AUP and swear filter are also swatted.