Here's the link to the article at tomshardware. I thought this quote was most interesting:
"Linux supporters know that, in terms of operating system rankings, the Top 500 list isn't even a contest any more. 391 systems on the list ran some variant of Linux, although a UNIX variant can claim #3: "ASC Purple," also from Livermore Labs. The highest-ranking supercomputer running Windows was #130, a Dell PowerEdge 1855 running a 900-processor cluster of Xeon CPUs, with a performance of 4106 GFlops/sec."