If you take a 1GHz, 1 GFLOP MIPS based core that uses 600mW of power, that fits the definition of a millicomputer (depending upon how much RAM you also add). Now if you put 6 of these cores on a single chip, along with DRAM and PCI-Express controllers and a high speed fabric interconnect for 10W it's quite interesting. Packaging almost 6000 cores on an interconnect fabric in a single rack takes it to the logical conclusion. Thats what Sicortex have done.
Even better, they have the *best* web site architecture tour I have ever seen. Its worth browsing it just for fun. Visit the page here, and click on the buttons to animate the architecture. Don't miss the "Linux" button and step through the Hardware Environment starting at the "Node Level" button.