Google's App Engine continues to evolve, and lots of steps were taken or announced at Google IO 2011 last week. I'll use this post to collect thoughts and evaluations as I think thought all that I learned.
This post on App Engine blog is a good place to start: http://googleappengine.blogspot.com/2011/05/year-ahead-for-google-app-engine.html
So, App Engine won't be as "free". App Engine pricing will increase, and the previously-discussed App Engine for Business has been folded into App Engine pricing tiers. Here is a current FAQ on App Engine pricing:
https://groups.google.com/group/google-appengine/msg/739169f799d8e69a? It makes some sense to me that Google has had a chance to learn how much its costs to run this service, and it seems fair to reflect that knowledge into the business model.
App Engine is no longer in preview mode. Also a good thing, this includes providing SLA terms, corporate support, and other features that will make App Engine easier to explain to enterprises.