Well if Simu goes with how they do PvP in Gemstone IV it will be something like the following:
Griefing is outright baned. If you kill someone without "cause" you likely will be sucked into the Consultation Lounge and have a nice chat about your actions. After 2 or 3 visits you would likely be baned from the game.
That said, there is open CvC (character vs character) if it is mutually agreeable. If someone steals from you, that is open invitation to bounce on them. In Gemstone they recently make a challenge verb (an OOC way of setting up a IC battle).
The general rule is if someone wrongs you, you may take actions against them for a 24 hour period. They don't encourage hold over grudges. Also, you must take care of the problem, no getting friends or other PC's of yours to frak them. However, if two large groups of people want to roleplay a conflict that is fine. If someone tells you they want out of the CvC you must allow it (unless of course they initiated something recently: attacked you, stole, etc.)
There are laws in the towns, if you cause harm to someone in town, even if they are a thief you have broken the law and can become wanted. Once the NPC police get you, you will be locked up in jail for a short time (a couple minutes) with all your possessions taken. Next, a NPC judge will convict you (their is no not guilty! LOL) and sentence you to either a fine or at your choice locked up in the stocks in Town Square for ridicule (folks can toss fruit at you and such). As a side note, if you fail to pay your fine in the alloted time, all your possessions are forfeit.
Overall I think the CvC works well in gemstone.
Chris