AMD Opteron 4100 processors (announced availability this week) represent a new class designed for the cloud. Imagine a 12-core server node at 100% utilization drawing just 130W. That is less than 11W/core at the platform level! (Supporting information for that).
More information: AMD Opteron 4000 Series Platform Press Kit
The best “nugget type” news report: AMD unveils new Opterons, Firestream add-in boards