I've played it a number of games run by a diverse group of GMs, and I have GM'd myself for a long time. I don't recall any of us having a Group Charter for our games. We do, however, have a general set of understandings about what the roles of the players and GM are, and sometimes a given GM might say something like "in my game the dice have to land flat on the table or you reroll". One of my favorite GMs, now that I think about it, made this statement when I rolled my first Character in his world: "By the way, I cheat." I took that to mean that he cheats when following the dice would wreck the story, and went along with it. We never could tell if he actually cheated or not, but it was understood that he *might* cheat. As Players we simply accepted this form of GM Dictatorship, mostly because his world was, from a fiction perspective, outstanding. So I'd say that game Charters can be flexible, depending on what the GM and Players agree is fair and good for the game. While I don't have a specific Charter, I do have some understandings:

1. The GM is the adjudicator of the rules and gets final say.
2. Players own their Characters words, deeds and motives.
3. The GM owns the back story and NPCs.
4. All dice are rolled in the open and the odds stated before hand.
5. The GM will not be obliged to provide stats on monsters or NPCs.
6. The story is important, but the dice ultimately rule.

If, as a Player, you can accept the GM Charter then great. If not, lets discuss. Maybe we can work it out. It is not a bad idea for the GM to have a clear idea of his Charter, even if he or she doesn't formally write it out as such. I'd also say it's helpful to no small degree to inform new Players what the Charter rules are.