It looks like there’s a race on to get anything and everything working in the cloud as Amazon Web Services and Oracle come together to deliver a certified solution to run Oracle 11g inside the Amazon EC2 hosting cloud. This means big things if you start to think of the possibilities now available, especially in the field of load testing or short, sharp bursts of massive computing power to achieve Oracle related database tasks. Oracle also allows you to transfer your existing Oracle licenses to your cloud instances as you cut them over to the cloud.
The biggest problem that I see integrating EC2 based Oracle instances with existing database solutions that are hosted elsewhere is raw IO throughput, getting lots of data from the cloud to your external hosting would be evil. Amazon would probably prefer that you host everything in their cloud to make all components local to each other. It all depends on how you want to leverage cloud computing technology to benefit your enterprise.
Not being a DBA, I’m not very informed on database challenges, but I’d be very keen to hear how replicating a database hosted externally to a database in the cloud would work and what concessions might have to be made to make work successfully. Any oracle database admins out there care to comment? 
From the Featured Partners page at Amazon.com:
Oracle customers can now license Oracle Database 11g, Oracle Fusion Middleware, and Oracle Enterprise Manager to run in the AWS cloud computing environment. Oracle customers can also use their existing software licenses on Amazon EC2 with no additional license fees. And for on-premise Oracle installations, AWS offers a dependable and secure off-site backup location that integrates seamlessly with Oracle RMAN tools.
Here’s also a link to the Oracle Cloud Computing Centre at Amazon.