[mkramlich]

while I agree that some of the strongest techniques for scaling are available on many platforms/stacks, you will generally have the easiest time of it on a Linux stack rather than say Windows. Only at the thousand-foot perspective does the stack not matter. But on the ground, where the devil is in the details, the stack matters quite a bit when it comes to what toys are available to you, what resources, what options.

[benologist]

I would say your familiarity with the stack you're using is what matters, both Linux and Microsoft platforms have been shown to handle massive loads with enough massaging.

I would also say it's a massive and on-going trial and error process to see what actually works, the biggest sites are still learning and falling over.

[rodh257]

Stack Overflow claims that by running a Windows stack they save money compared to a LAMP stack due to its better performance (MVC2,SQL2008) outweighing the initial cost. I think they talked about this in their Google Tech Talk (Joel Spolsky).