http://highscalability.com/blog/2009/8/5/stack-overflow-arch... http://highscalability.com/blog/2011/3/3/stack-overflow-arch...
My two take aways are, generally you can make anything scale, cache like hell, and I personally don't see enough value in .NET to justify the licensing costs to roll it out initially or the long term.
Important part isn't caching. You can just create HTML copies off a page and serve them through a fast server, that is a very easy cache.
Difficult part is smart caching, cache getting updated when they need to be and persisted properly to the DB. These guys have nailed it in my opinion.
I often lookup these guys and optimize my own sites and have been following them since their beta phase.
http://www.microsoft.com/sqlserver/2008/en/us/pricing.aspx
Yes, BizSpark makes it free, but that basically locks you into the platform long enough for you to rely on it before you start paying those prices.
This old classic applies to business models as well as software: http://www.joelonsoftware.com/articles/FiveWorlds.html