When you wait for an answer, it would be nice if a message will be popped and say: "John is typing an answer/comment" as in Google Talk.
It is not interesting. What actually matters is a real answer. Not people trying to answer.
Given that I've been often preceded by another poster who said the same thing I was writing, I guess I'm not the only one that did not submit an answer because someone was faster.
That would mean too many notifications for things that will not be concreted in an answer.