This tweet from former AppEngine dev Brett Slatkin caught my eye: https://twitter.com/haxor/status/411351463806263296
I still think Dynamo has a ways to catch up in terms ease of use to GAE, but it provides the performance, scalability, and replication like datastore.
It'd be an interesting test to try setting up a simple stack of psql/nginx/memcache and your go processes behind, and serving up the same data from it, to see what sort of performance you get, but I understand why you wouldn't bother if your app is somewhat tied in to the datastore already and works fine for you as is. Just out of interest, did you start on something else and move over to Google App Engine for performance, or start there?
Yes, I could set up a simple psql stack. But I would lose automatic multi data center replication and infinite scaling, so that's not a win. My database hit 500GB in a few months. I don't want to deal with scaling up psql instances when it doubles in size over the next year again. See my first post linked below about when newsblur hit the HN frontpage and was effectively down for 3 days due to load. It's because psql doesn't scale in that direction.
http://mattjibson.com/blog/2013/06/26/go-read-open-source-go...