Just an introductory thread here - viewtopic.php?f=11&t=18494 which gave me an idea.
Part of what made me stick around on MLK when I initially joined and made my little intro thread was just how friendly and welcoming everyone was at the time.
So the little idea I am throwing here is, why not have a specific group of people, either by a new usergroup or more appropriately, just a little icon perhaps in their signature which indicates they are part of the greeting team? And people on said team, would have to regularly welcome new members.
I think having a little more of an emphasis on it, would prevent things like the thread I posted above, where someone may not feel welcomed (it makes the forum look rather inactive, not to mention it is just a bit discouraging.)
And then people would see the little icon, and think "Hmm I could check the introduction area and greet some new members."