Ive used it on each of my game lunches it can work well if your Ads is nice and you pick good keywords and all that stuff, but if if you don't it's a waste. so when creating your ads be precise. For me just interacting on twitter and such has been more helpful though.
Yeah i think you do need to be precise with facebook, i've seen comments about fake clicks by bots with fb ads that add fake pages and friends to look "real" so it consumes an advetiser's funds. So since my page is for a game, I've also added the condition to show people who have "played a game in last 3 days", which should eliminate bots.
Thanks for the twitter suggestion, my twitter account is pretty inactive