What is "good enough" security in your mind when designing a network?

I realize that this is a pretty nebulous and open ended question. There are definitely many needs/requirements for networks (PCI being one of them), and of course not all networks are the same in their needs for security. I just felt that maybe it would be good to have a discussion about this just to see where we all kinda are in this oft heated topic.

However from what you guys/gals have seen, where do you feel is a good point of compromise of security for most use cases, and how have you/your company/your group achieved it?

Thank you :)