Quite often I have run into situations where I had an extensive talk with a newbie (about SO and/or programming itself) using the comments. Since you shouldn't use the comments to further discuss things (which are often off topic from the original question), I'd like to use the chat for those discussions.
As a matter of fact if you do use the comments to discuss something, you get a notification which tells you to move the discussion to a chat-room.
Unfortunately, most of those users don't have the required 20 reputations to talk in chat, so you also get this fancy orange box telling you that you can't move the discussion. This normally leads to using the comments again.
Don't get me wrong at this point, I'm NOT asking you to change this (I actually think it's a good thing).
My idea would be, that a user who has enough reps to talk in the Chat should be able to invite a user who doesn't have enough reps into a private Chat-room (just for the two of them).
The user with the
<20 reps would only be able to talk in this very room, e.g. would receive a "temporary privilege".
Edit As nhinkle pointed out, this is already possible but you need to be Moderator and it requires multiple steps. This gave me the impression that it shouldn't be that difficult to realize.