as far as give aways and promos are concerned, they rarly work and generally make people, (loosers, which are vast majority of players) angry at you. there is just too much cheating-hacking etc, for it to be worth while and it seems like the winner is almost always a hacker and the entire community will know except for the developer. i would skip it, unless you are desperate to get your app some attention. alternativly, you could give away in game bonuses, like custom icons, upgrades etc, things that can be given en mass to satisfy as many as possible of your fan base at minimum cost, then the majority will feel like they were rewarded and the cost to you would be minimal.
