This is how to upgrade to Oracle Weblogic from Oracle Application server 10.3.*. Video from Oracle developers Day, February 2011.
Using smartUpgrade utility to copy your OAS settings into corresponding Oracle WebLogic setup. I like that you don’t have to install WebLogic Server before,
ssmartUpgrade utility does it for you and leave original Oracle Application Server 11g instance intact.
I am planning to give it a try on my Solaris box, will post my experience later.