But then how soon do GMs start doing pre-sign up? And we would run into the same issue of timezones when the GM announces they are taking pre-sign ups?
I've also missed a few games due to not checking PC for a day or being asleep, though I think each time was for one of the smaller games so it would make sense that those fill up faster. I agree that both would have pros and cons, neither being truly "fair".
Maybe rather than making a game a specific size and allowing only a small group of people to join (or in the case of large games, waiting to get enough participation) there could be some way for the GM to see how many people would be interested in joining it so that they can build the game to roughly fit that amount. Of course, some people who initially said they would want to play might decide not to as the game starts, or we might get someone new to UG who wasn't here for the initial polling but wants to join. So the GM just needs to have a handful of vanilla characters (oh no, not the dreaded 'nilla role!) to allow additional people to play, or as a buffer if not enough people signed up. This might require waaay too many polls though, and we'd turn into a subforum that takes polls and occasionally plays Mafia :p