Google today gave word that developers can now use automatic leaderboard tamper protection "to automatically hide suspicious leaderboard scores." That'll keep cheaters from seeing their scores shoot to the top faster than they should. (Though obviously my Sky Force 2014 process is legit among my small circle of friends.)
Google notes that tamper protection doesn't work if you're using shared iOS or Web implementations, so it's not perfect. But it's one more good tool for Google Play Games Services.
More: Google Play support