How to properly increment a counter on Google App Engine

Reading this makes it sound as if implementing trivial things that would be "easy" in traditional environments would be a total pain in the ass in GAE.

I would suggest looking at this implementation: http://appengine-cookbook.appspot.com/recipe/high-concurrenc...

My current counter system uses a single datastore entity per counter and uses the new CapabilitySet API to check if memcache will go offline in near future.

You can also use the newish Appengine feature for Task Queues (http://code.google.com/appengine/docs/python/taskqueue/)