1) I don't understand their pricing scheme, does gamfeed use the free or the paid? (because currently I'm seeing 2 price lists: http://code.google.com/appengine/docs/billing.html and http://www.google.com/enterprise/cloud/appengine/pricing.htm...)
2) AppEngine Datastore: have you ever need to modify your model in a way you have to run a transaction over a large number of rows? If yes, would that hurt? (or, another case is if you had encountered a bug in your code that mistakenly recorded the wrong data thus you have to "clean them all").
3) I saw your code regarding code optimization, would that cause the code to become a bit brittle by not encapsulating the caching somehow? Like, spreading the cache at various level in your code.
2 - datastore query is expensive but memcache works great, so cache frequently accessed data
3 - i make sure that whenever i put() any data, i immediately set Memcache, and before making any get() from datastore, I try get Memcache first, this should not cause issues.
My question for point #2 is in the line of the need to perform data migration actually.
Let's say you have a bug on your code in a way that the data stored currently are wrong and you need to fix them up by performing a batch update. Would that hurt you in terms of cost? How would you handle such situation?
Or let's just say that your user profile data model needs to be re-jiggered to support a new feature (adding columns, changing current columns, etc).