I've just started as a Developer Advocate for Google App Engine and there's been a lot of talk of "lock-in" recently. Google will have more to say officially in the future, as obviously my blog isn't the place to read about Google's official position, but I would like to point out the following things that have come up in conversation that people didn't know:
- The development kit is open sourced.
- All of the documentation for App Engine is CC licensed.
- Much of the underlying technology has been described in academic publications.
- Some of that underlying technology has been open sourced, such as protocol buffers.
Also, you can see that other issues are on the roadmap to be addressed, such as bulk upload and download.