GAE Logging

By default GAE's admin console supports fine control of the Java Logging Framework (JDK Logging). The configuration format can be learnt from the ${JDK_HOME}/lib/logging.properties file.

http://code.google.com/intl/en/appengine/docs/java/runtime.html#Logging

http://docs.oracle.com/javase/1.4.2/docs/api/java/util/logging/LogManager.html

GAE in Action

Some Concerns in using GAE as your Backend

1. No sockets. The API does not allow Java sockets. You may use URLFetch API instead.
2. No relational database, not even deploying a sqlite db as resource file due to the read-only restriction of resource file in GAE. (This is not true now as Google is rolling out Cloud SQL API which support MySQL-like relational database.)
3. HTTP response/request data size limits : 10MB each

Facebook JavaScript SDK
http://developers.facebook.com/docs/reference/javascript/

The Unofficial Google App Engine Price Change FAQ
http://blorn.com/post/10013293300/the-unofficial-google-app-engine-price-change-faq

Scheduled Tasks With Cron for Java
http://code.google.com/intl/en/appengine/docs/java/config/cron.html

Running PHP on GAE

Steps to run Quercus (Java-based PHP interpreter) on Google App Engine:

1. Download Resin-4.x.x from http://caucho.com/download
2. Copy lib/resin.jar to your WEB-INF/lib 
3. Add com.caucho.quercus.servlet.GoogleQuercusServlet as a standard servlet in your web.xml
4. Add index.php pages to your web-app

Reference:
http://blog.herbert.groot.jebbink.nl/2009/05/using-php-on-gae.html
http://wiki.caucho.com/Quercus_Google_App_Engine