I have given myself a date of May 31st as the last day to have everything ready (printed and packaged) and to submit my game for review with a game publisher. But as I draw closer to that date, and with more play tests and more collaborations/peer-editing I find that I can tweek the game just that much more. I would imagin that it is endless because we all love to create house rules and "that would be cool if" moments with our own creations.
When do you finally decide to put the stop on a project and finally submit the darn game?