I personally prefer to not to see separate servers. A balance can be met with just one server, as has been demonstrated my numerous other MMPORGs, to allow the the full spectrum of hard core PVP all the way down to pure PVE. But even in PVE there needs to be some risk involved....weather, mobs, pirates, whatever....just something.
Balancing PVP vs PVE will be the easy challenge. Balancing the economy will be the tough battle, especially as NA scales up from day 0 to (hopefully) a massive player base.