Tiny Tower is awesome. It's free. It's something you can just pull out of your pocket and play for 30 seconds and then do something else. It's basically designed around that idea. Sure you could pay money and get more done in a few minutes instead of waiting day after day, but that's not the point.
In fact, it's not the point of this post to expouse the greatness that is Tiny Tower. I'll let the developers behind the title, NimbleBit, explain why the maker of Farmville and other Facebook bull shit is ripping off Tiny Tower: