2 years ago, this question was posted here at Gillies's blog, on date of 2009-05-15.
Future for geospatial on App Engine?
At that time there was no news relating to any apps of GIS web services using Datastore (Google's App Engine).
Is there any new information on GIS and App Engine over last 2 years?
In general, what cool map making and spatial querying web services use Google's App Engine Datastore instead of typical relational database ?