I’ve had a chance to research the Little Green Server ideas more, and I think Via and AMD are potential better platforms for low power servers.  Tom’s Hardware has this post on Intel Atom vs. AMD Athlon.

With the development of the Atom processorhttp://en.wikipedia.org/wiki/Intel_Atom , Intel introduced a totally new chip design that consumes very little energy. AMDhttp://en.wikipedia.org/wiki/Advanced_Micro_Devices had to strike back, and did so by clocking down its Athlon 64http://en.wikipedia.org/wiki/Athlon_64 , employing the K8 micro architecture, down to the lowest possible frequency of 1 GHz. The Athlon 64 2000+ runs with a core voltage of 0.90 volts and uses just 8 watts. As a result, the CPU easily operates without a fan. If you drop the 8 W Athlon 64 into a motherboardhttp://en.wikipedia.org/wiki/Motherboard based on the 780G chipset, then the system hits power consumption numbers that, in our measurements, are below Intelhttp://en.wikipedia.org/wiki/Intel_Corporation ’s Atom desktop solution. We were even able to lower the core voltage by 11%, without stability problems, and the power analyzer read lower numbers. Interestingly, AMD’s Athlon 64 2000+ processor, unlike Intel‘s Atom CPU, is not embedded in the motherboard. It can be run on any board with an AM2 or AM2+ socket.

Compared to Intel’s Atom, which runs at 1.6 GHz, the Athlon 64 2000+ is clocked at 1 GHz—60% lower. Despite this, the Athlon 64 outperforms the Atom in several benchmark tests as a result of its more efficient K8 architecture. In addition, the energy consumption of the entire system is lower, and that’s what really matters most.

In the conclusion.

In our Munich lab’s duel of the energy-savers, the AMD Athlonhttp://en.wikipedia.org/wiki/Athlon 64 2000+ beats the Intel Atomhttp://en.wikipedia.org/wiki/Atom 230 in energy consumption and processing power. Each of the systems was based on a desktop platform. The Achilles heel of the Intelhttp://en.wikipedia.org/wiki/Intel_Corporation system is its old system platform with the 945GC chipsethttp://en.wikipedia.org/wiki/Chipset , while AMD offers a more modern 780G platform.

The energy-saving solution from AMDhttp://en.wikipedia.org/wiki/Advanced_Micro_Devices offers more possibilities: it has three times as many SATA ports, possesses better onboard graphics performance, and can also support two monitors. Unlike the Intel solution, an HD resolution (1920x1200) with high picture quality is possible through DVI/HDMIhttp://en.wikipedia.org/wiki/High-Definition_Multimedia_Interface ports. And early information suggests that the AMD Athlon 64 2000+ should cost close to $90.

ExtremeTech has an article building an Intel Atom based PC.

Intel's Atom has generated a lot of attention. Some of that attention has been positive: Intel building an x86 CPU whose primary design goal is very low power usage while maintaining good performance. On the other hand, Atom has been criticized for given up some key performance features, such as speculative, out-of-order execution.

Still, Atom has garnered some interesting design wins, including appearing in some of the tiny laptops first pioneered by the ASUS EeePC. Atom's most recent appearance has been in MSI's latest sub-laptop, the Wind.

What about Atom on the desktop?

First, you might ask why you'd want Atom in a desktop configuration. Its very nature suggests that performance would be limited. At 1.6GHz, and lacking out-of-order execution, performance might be pretty low. Other aspects of Atom, such as simultaneous multithreading (Hyper Threading) and a fast SSE2 floating point unit, might mitigate some of that.

in their conclusion, they get to some of the ideas for a Little Green Server.

In the end, a PC built around an Intel D945GCLF makes for a fine, light duty Web-oriented PC. It could even serve as a light duty home server, with the right storage gear. It is not, however, well-suited for even casual gaming, and we'd hesitate to run a full-bore office suite on it. Still, at 46W running flat out, it won't break your power budget.

Intel is really just dipping its toes into this market. We'd love to see more home-server oriented boards, with onboard RAID and no parallel ATA ports, for example. The system is also pretty noisy; the tiny CPU cooler isn't exactly quiet. Still, the D945GCLF will make an interesting test bed for anyone wanting to explore Atom's capabilities.

Another interesting review is from AnandTech and Asus's EEE Box.

Tom's Hardware has a review of the Intel Atom chip.

Intel is rumored to be  releasing dual core Intel Atom's in Q4 '08.