yep, been caching it from the beginning. the problem is purely usage. it went viral (top 50 in 5 countries in europe and top 100 in 30+ countries worldwide) and hit quota limits... google being google has no simple way of reaching them.
quick update: google and their api is garbage. ive updated to another provider on a paid plan that costs less than them, has about the same size library and allow us to file support tickets in case something goes wrong. oh and student discount on the api helps make it 50% cheaper woohoo!!
Would you like to tell us a bit more, perhaps? E.g., what's the name of your app? What's its purpose? A book recommender? Book search? Onlinee book purchase assistant? S.th. else?