Another subs 2 cents worth if I may:

I agree with pixie and tessa. That is the absolute worst, and in the beginning of my training Master was forced to use it a time or two. We first met in a chatroom and hung out there often, so he would come in and politely greet me and then totally ignore me until it was my bedtime when he would say goodnight. I cried myself to sleep many the nights. The problem with this discipline (and another if you are RL, which is to chain the sub to the foot of the bed and make her sleep on the floor) is that as far as my Master is concerned, he was being punished as well because he was being deprived of my company which he actually does enjoy. Still it was very effective!
Another that I truly learned to dispise is a writing task. I don't mean having to write "I was a bad sub and disappointed Master" a gazillion times. He would give me actually research assignments complete with bibliography and footnotes. Gargh! Awful. Hope this helps. "Peace" ~blizz~