There's a great talk about this from some guy at Digital Illusions. He found some definition of what a "game" is and compared that definition with Farmville, it failed on every single bullet. I can't remember the exact details but it contained things like it has to be challenging, a skilled player should easily beat a newbie, not requiring grinding. What's interesting is that the definitions are not designed with the sole purpose of bashing farmville, all of them really make sense and origin from even before computer era.

If somebody knows where to find the talk please post it, my google-fu is weak today. He also compares the iphone to a swiss army knife and the ipad to a "swiss-army-kitchen-utensil" (i.e too bad to be really useful and too big to fit in your pocket). The talk was just a few weeks after the first ipad release. It also contains alot of other talk about the future of gaming for the general masses, facebook games and gaming anything in life(like shopping), etc. If that's enough to trigger anyones memory.