I think it's really important that the punishment be appropriate to the situation. An infraction that early in a relationship might earn a mild punishment would perhaps merit something more severe as the relationship progresses and I would supposedly know better by then.

I've only been punished twice - and we found out the very first time that disappointing him is one of my biggest fears. That time wasn't even an actual punishment in the end - simply the threat/suggestion, which made me feel horrible about letting Him down - and then when I was extremely upset about the prospect - a simple "I forgive you". That emotional reaction on my part to the realization that I'd let Him down was the meat of the punishment, and it was very effective.

The second time - well, suffice to say that I'll remember to ask for orgasms when I'm told to. I felt terrible when He asked me, in a gentle tone of voice, "How many times did you cum" and I replied "three" and then from Him - "How many times did you ask?" and I realized - two. Writing lines is boring. And publishing them is just plain embarrassing. But it worked.

My personal goal - never to disappoint Him in any way again.