Then you should have a look at David Peake’s blog. He is the product manager for Oracle Application Express (APEX) and currently looking for big Oracle APEX applications or as he says it in his blog posting: The Bigger the Better!
We know that Oracle APEX scales well and can handle lot of concurrent users without requiring a lot of hardware. AskTom, apex.oracle.com, Oracle Metalink or the Oracle internal ARIA are good examples. But the more “real world” example they/we can reference if someone doubts the scalability or if it can be used for “missing critical” applications, the better!
Check also out his posting about the access statistics and hardware used for apex.oracle.com.