Maybe we can have a mix all of the ideas proposed here,and built a great system for PVP.
Noobs can?t be killed/duel/robed up to level n.
Chars can?t be killed/duel/robed if the difference between then is more than (less say) 10-15 lvls
Some places should be safer, NPC police? or just god eye, and other should be more dangerous, above rules change for a wider level difference, noobs protection is removed...
and finally is somebody really really bothers you , call a honor duel... then none of the above applies, the other character should be forced to fight by the same law that in other circunstances will protect him, or at least put him in jail...(have no idea if there is a jail )
finally, thiefing, should be restricted in same manners, but shouldnt be so regulated that you can?t take a thief profession... and what about assasins?, spies?