I am sure every one consult/refer to Oracle documentation very frequently.
In addition to 2 Day DBA, today, I have found couple of 2 day books added to the Docs. Library of 10gR2.
These books provide background information for new users:
2 Day + Real Application Clusters Guide
2 day + Performance Tuning Guide.
This is really a good idea for the new users as instead of going across many pages to find the information, now, they can simply get digest concepts in few pages.
New users, who are keen to learn about RAC and Performnace Tuning, they simply can start with those books.