I'm a ruleslawyer from 3.5 D&D, but I've since branched out into many other systems. I currently play Pathfinder for the most part.
I believe that the GM's first job should be to know the rules. Games are much more fun when rules are selectively ignored or fudged, but it's important to know the implications of rules changes before making them.
Q&A for gamemasters and players of tabletop, paper-and-pencil role-playing games
Q&A for power users of web applications
Q&A for professional and enthusiast programmers
Q&A for professional graphic designers and non-designers trying to do their own graphic design