Very small, but frequent DB updates. I wasn't responsible for the software, but simply put, it was a backend for a not-so-popular Chrome extension, which was doing authentication and persisting some state (a few integers). I'm sure the architecture could've been optimized specifically for AppEngine to reduce the cost, but why do you need to invest so much effort in optimizing something so basic that works just fine on EC2 m1.small or Digital Ocean for few bucks per month?
