Link:
http://forex-tester1.blogspot.com/2010/12/limitele-google-app-engine.html
In summary, before Google App Engine can be used for real web applications, the following issues have to be addressed:
1MB limit on data structures must be removed.
Quotas must be handled optimistically, without crippling applications at the very moment that they should be benefitting from The Cloud. The "intelligent throttling" "feature" and short-term CPU quotas must be removed.
The 1,000 item limit for offsets in queries must be removed.
Support for long-running processes must be added.