Yeah, banned folk, deleted users, &c. Sooner or later we'll start taking out the people who registered way way long ago and then never used their accounts, too - maybe pretty soon for that, as we're getting close to the six month mark from the "official" opening.
Space has now been made for you to add your Twitter username to your profile. SO! Go edit your profile! Right now it's only in the profile page. I'm not sure if we're going to add it to thread/post displays or not - I'm leaning towards not.