I can just see them having a pool of IP's that they will cycle through after detecting a block, it will take a lot of work on Netflix's part to keep up with this, as Cods said it really is a cat and mouse game. Blocking VPN access is a different thing again, which I seriously doubt they would block (but again easily fixed) and there is no way they can tell where you're coming from when using a VPN. They could tie authentication in with region content but then that would mean if you travel overseas you would have access to content you shouldn't have access to.
I am really scratching my head as to what they can feasibly do, I think they might block some proxy/dns providers which will cause short term disruption so they can say l"ook Fox/Sony/Universal etc, we are doing something".