That said, I once went to a freeform game at the local con here in St Paul where the event description was "Chris being arbitrary." I had never played with any of the players before (and haven't since, either). It was great fun , and I think the event description was an effective piece of communication. It said "don't show up unless you're willing to go with the flow." A number of the freeform games from my college days that I played in LA-area conventions were more hit-or-miss (but there were notable hits), I think largely because the communication was lacking. IME, if you show up to a freeform game and everybody wants to be in the game that the GM wants to run, you are 95% of the way to a great game. In fact, I think this statement holds for just about any RPG at all, not just freeform.
And I think it's this element that is the strength of games like Dogs in the Vineyard and My Life with Master. The game rules themselves specify quite narrowly "what game the GM wants to run" when he invites everyone over for a game of Dogs. This is also the weakness of those games: by specifying this narrowly, they become inflexible. If you don't want to play the narrowly-specified game that Dogs is, you're out of luck. That's why Star, Moon, and Cross takes a more toolkit approach: through the Gaming Preferences Discussion part of the game, it helps the players make their own game specification. This fails in a different way than Dogs fails: it fails when the players fail to communicate effectively with each other -- either through simple miscommunication, or because the Gaming Preferences section omits important items of discussion. IME, this approach fails most often through ambiguity in communicating the game's specification. Players with flexible game preferences will tend not to find that this is an issue; players with firmer game preferences will tend to have more trouble with this approach.