Just a bunch of link s on this topic:
http://www.settlersoman.com/vmware-vsphere-basics-understanding-resource-pools/
http://www.yellow-bricks.com/2010/02/22/the-resource-pool-priority-pie-paradox/
http://www.yellow-bricks.com/2010/12/14/shares-set-on-resource-pools/
http://www.yellow-bricks.com/2010/02/24/custom-shares-on-a-resource-pools-scripted/
http://www.settlersoman.com/vmware-vsphere-basics-understanding-resource-pools/
http://download3.vmware.com/vmworld/2012/top10/vsp1683.pdf