I haven't decided if PvP will be allowed in specific areas or vice versa.
There is the "warzone" idea, with other areas like Colosseums designated +PvP as well.
Then there is the idea of having safe zones, and everything outside of those being +PvP.
The biggest problem is the DynMap... since you can always see where everyone is. I may be able to specify that players are only visible in certain areas... which could be cool.