There’s an interesting article on High Scalability discussing the use of .net within MySpace: Did the Microsoft Stack Kill MySpace? The discussion is based on this post by Robert Scoble: MySpace’s death spiral: insiders say it’s due to bets on Los Angeles and Microsoft.
The conclusion is that you can’t blame the microsoft stack for MySpace’s death, but I find this piece of the conclusion quite contradicting:
The stack isn’t the real problem. … You can’t exist at this scale without transforming everything you touch to meet your specific needs.
How are you going to transform everything, if you’re using closed software? Google can and has modified Linux to meet it’s specific needs, Facebook can and has modified php to meet it’s specific needs, and there are more examples.
Opensource allows you to transform everything when you need to.