Ever noticed that the DBA gets assigned the task of making a product work, if the product has the name 'Oracle' in it?

One of the more common things I see is the DBA being asked to support Application Servers. I plan on adding some basics in this page but need some guidance on what is important.

As a DBA what is more important:
- basic understanding of App Servers and J2EE containers?
- installation of an application server? (basic app server, portal, infrastructure, forms, reports, SOA ...)
- structure and logs?