So you would type out the word "nod" once in a while, just like you would nod your head during a physical conversation? That's curious. I've never seen that before - I don't use chat/IM a whole lot though.
I know a few people who do it. I can see the point... sometimes you say something and you aren't sure if the other person has gotten up to use the bathroom or is otherwise distracted, or if they are thinking of something.
Personally, I prefer 'thinking...' or 'looking' when I ask a question and there will be a delay, but I can see the point of 'nod'