Mesages such as this are very common in all rooms: http://chat.stackoverflow.com/transcript/message/1362574#1362574
We have the data available to determine if a user is new, so what if we had the option to set up room guidelines and so forth when they enter to be predominately shown? I know some rooms have the rules, but it's obviously being ignored in many cases, and others, might not be important to who's in the room most of the time.
It could be a floating box showing some text, or whatever.
What "new user" means in this case is, new to that room. For instance, that user is familiar enough with the site to have a respectable site-wide rep, but the individual rooms may have their own social protocols or otherwise. We have, in the database, information on how much participation this person has with a room. We can detect their interaction in any particular room, or rooms in general.
That detection would then trigger a room's setting some where-- if they so choose to configure one-- that welcomes new users and gives them the overview of the room, an FAQ about questions, etc.
I know this room has a lot of questions where people don't get explaining the right details of problems, using common tools that are very helpful, if it's okay to ask, don't come in and say "I know you're not PHP but here's a PHP question..." etc.