If the GM role provides content for achievers (levels, power rewards...) then either you''ll have a community of good GMs (socializers) that hate the system, or a community of bad GMs (achievers) who love it. Neither of them is good for a game 
Luctus that''s a really good idea, non-absolute ratings.
Hmm... what kinds of features would be good for a GM client? There''s all the regular stuff that comes with most map editors: creating items and NPCs, monsters, traps and the usual map features, draw the maps as the players move around, like chosing the next room or something - BTW a GM can''t draw the maps tile by tile on the fly, how could this be done so that it''s easy but at the same time all rooms don''t end up being xerox copies of each other? (Neverwinter Nights suffered a bit from this)
Most of the actions that the scripts have access too should also be available for the GM - opening doors and manipulating the environment, changing HP or adding buffs to the players/NPCs/whatever, ordering NPCs to do stuff. Being able to possess an NPC and play it like any other player to chat with the players and stuff should also be available. There could be a nice built-in dice roll utility to help the GM make decisions. Anything else?
