After setting up an app in the google app engine with a domain name, I found that accessing the domain via the naked domain name (no www.) would not work.
Worked:
http://www.mydomain.com
Didn’t work:
http://mydomain.com
After search for a while, I came across this answer:
http://www.google.com/support/a/bin/answer.py?hl=en&answer=91080
The solution is to forward mydomain.com to www.mydomain.com with your domain registrar. After doing this, it worked as expected.