A facebook app is an awesome idea but if the game catered towards the app and started changing just to appease the facebook players that would be terrible. Also I worry that if there was a facebook app it would be too different from the website which is why maybe rather than making a facebook app so that it can be played on facebook, make the app different but similar, not as good, but fun, like an arcade game and spam add for the website so that the user base will grow while not messing with the basics.