First they laugh at you…
I found this article in “Network Computing” pretty interesting, although not exactly for the content. Just the framing of the whole article, with Microsoft is touting the fact that they’ve managed to achieve performance parity with Linux on some HPC benchmarks as an achievement (and putting up a graph that shows they are still at least a few percent behind), shows how dominant Linux is in HPC. Also, the article says:
The beta also reportedly includes optimizations for new processors and can deploy and manage up to 1,000 nodes.
So in other words Microsoft is stuck at the low end of the HPC market, only usable on small clusters.