What I'm personally working on for fun is GAE as the business layer of a traditional 3-tier database-backed web application, perhaps a combined scoreboard and repository for a simple game.. By doing so, I think it will be possible to avoid the issues of Google lock-in as well as most of the benefits of scaling. I think the following components will allow me to avoid google lock-in with minimal expenses.
- A cheap postgres server
- Web service for database (PHP?)
- GAE to talk to the database and host games
- RIA client to minimize work in GAE
The RIA client should consist of static files, most likely compiled Flash or GWT. I suspect that GAE is not the best way to serve up the client, but it's probably the most reliable free web hosting that I have now that Google Page Creator is going away.