There seems to be some confusion on what a GM actually is, so I figured I would weigh in on this topic to clarify what I consider are a few misconceptions.
I see a lot of people saying that GM's give ruling on zone fights, mentioned both here and on SL. However as people are all too fond of pointing out, GMs have no power to do anything at all.
Game Master = Dungeon Master.
This is the person who comes up with story line, creates events and implements them. Advertises and drums up enthusiasm among the players of the game to participate. Makes accommodations for everyone to have something to do during the event and tries to see that all are able to enjoy themselves. The GM is not a player...this means that it is not the GM against the players in a win/lose situation.
Rather, the GM has to be aware of the player's skill, craft foes and obstacles that meet their skill level but do not exceed it, and then set up situations in which a player character can face a challenge and use their skills, talents, and creativity to cope with it. The GM helps the player grow their character. It is important not to create tasks too hard or too easy. Rewards that are too weak or too abundant are also a thing to be avoided.
IT should be noted...ANYONE can do this. I did this for years without the GM powers and it is silly people who think differently. Additionally...zoning is not RP. it is a part of RP. Any action your character performs is RP and it is so much more than just fighting.
There are a TON of people on SL who are starving for RP to do that is not zone fighting and war. There are many many more people who are not powerhouses and need to grow in RP and experience other adventures besides zoning.
As far as rendering decisions on zone fights go, anyone that both parties agree upon can be called in to arbitrate. It is preferable they know how to RP and to zone and understand the rules of game play.