With the new quad core cpus shipping in August, you can now upgrade from dual core to quad core, without any other upgrades.

AMD’s Barcelona will enable datacentres to double capacity without upgrading power supplies or cooling systems, the company has said. It also includes hardware support to speed virtualisation, providing a boost to server consolidation.(source)

This is a great potential for large data centers which have already deployed a large numbers of dual core systems. With no need to replace power supplies, each system could be upgraded with minimal downtime.