Depends which drive is in it. Some of the older ones did region checks in hardware so you had to replace the firmware (that was the case on the original SuperDrive 12" PowerBook). On the current MacBooks the region check is in software so VLC works great.
On a Mac you are allowed to change regions 5 times, total, over the lifetime of the computer. So the prime minister could have watched all 25 classic movies, if he didn't alternate with other films in between :-)
I've been able to play European DVDs on my (N. American) Mac using VLC.
This is why I came back here VLC, the free software media player can play region encoded DVDs. I can make sure it DID that sometimes back. Never wanted to check it recently for some reason.