When my treasure neglected twice in one week to contact me for a whole day, causing me to worry and spend a lot of time trying to locate him...something humiliating for ME....I had him write 100 lines for me: "I will remember to contact my Domina every day so that she does not worry." I had him show his pages to me with the webcam. And it worked for us. He was reminded of his submission, and his responsibilities, and I was able to get free of the anger he had caused. I had felt insulted, taken for granted, and humiliated by his disregard for me and my feelings, because he had gotten caught up in something else and had not even given me a single thought all day.
So, his punishment. I always thought punishment like this was something you did to children, but doing it to my sub, while it may seem childish, establishes that he is serious about submitting to me, and it gives me a chance to get over my anger. The punishment is done, I see that he sees my point, and I don't have to stew, or think about how to get revenge. It is done and I can forget it. We both can move on from it immediately.
So I think using punishment is a good thing to practice and refine. And a bonus: It is a workable part of managing our relationship online.
More thoughts on punishment: http://subservient-husband.blogspot.com/2010/06/punishments.html