For the ones looking at an easy reading and first good approach to Oracle VM Manager and VM Servers, I would recommend reading the following book even so it was written for 2.1.2 whereas we can use now Oracle VM 2.2 :
Oracle VM Manager 2.1.2
Manage a Flexible and Elastic Data Center with Oracle VM Manager
Learn quickly to install Oracle VM Manager and Oracle VM Servers
Learn to manage your Virtual Data Center using Oracle VM Manager
Import VMs from the Web, template, repositories, and other VM formats such as VMware
Learn powerful Xen Hypervisor utilities such as xm, xentop, and virsh
A practical hands-on book with step-by-step instructions
Oracle VM experts might be frustrated, but to me it's not aim to Oracle VM experts, but to the ones who needs an introduction to the subject with a good coverage of all what you need to know.
This book is available on https://www.packtpub.com/oracle-vm-manager-2-1-2/book
Need to find out about Table of contents : https://www.packtpub.com/article/oracle-vm-manager-2-1-2-table-of-contents
Discover a sample chapter : https://www.packtpub.com/sites/default/files/sample_chapters/7122-oracle-virtualization-sample-chapter-4-oracle-vm-management.pdf
Read also articles from Tarry Singh on http://www.packtpub.com/ :
Oracle VM Management : http://www.packtpub.com/article/oracle-vm-management-1
Extending Oracle VM Management : http://www.packtpub.com/article/oracle-vm-management-2
Hope you'll enjoy this book as a first approach to Oracle VM.
For more information on Oracle VM :
Oracle VM on n OTN : http://www.oracle.com/technology/products/vm/index.html
Oracle VM Wiki : http://wiki.oracle.com/page/Oracle+VM
Oracle VM on IBM System x : http://www-03.ibm.com/systems/x/solutions/infrastructure/erpcrm/oracle/virtualization.html