I saw something interesting on one forum I saw. They had a mod that when a person registers for the forum, it automatically creates a "Username, Welcome to the Forum" topic in a designated forum (usually the welcome and introductions forum). The post welcomes them to the forum and invites them to introduce themselves. It sets the username to be the administrator (or whatever user you want it to be from) so that it looks personalized and from a real person.
Looking at that forum it appears to work, with people responding to the post thinking that the administrator had just welcomed them personally to the forum.