In my opinion, punishment isn't meant to be enjoyable. Play is meant to be enjoyable. Punishment may involve certain elements of play, but it's meant to serve as a reminder that a boundary was crossed and there are reprocussions for that action. Punishment is hard on both the submissive and the Dominant. It shouldn't be pleasureable for either party.

I suppose though that it is possible to enjoy a punishment if the point of the punishment was understood. Punishment doesn't have to involve elements of enjoyable play though, (spanking...etc) it can be entirely mental, or entirely physical, or a combination of both.

I think it depends on the individuals and the love and trust they share between them. It also depends on what the punishment is and the action that brought about the punishment.