Hopefully this is the real deal and not an abstraction on the current datastore. When using the datastore in a relational way, you get some pretty horrid performance.
The "free scaling" using appengine datastore is nothing more than theoretical at this point. The service has severe datastore latency problems and non trivial downtime. Looks like using RDBMS, solves both these issues for now, while Google can ponder around long term solution for the bigtable access.
