Yahoo:PHP+C++ Amazon:Perl/Mason+C++/Java

This is true even within single applications. Yahoo mandates PHP at the surface, but uses C++ for most back-ends because they need to handle a few billion page views per day. Amazon too has lots of core computations in C++ (and even Java), yet uses Perl and Mason for the front end. A reasonable division of labour at the biggest sites on the internet.

From: http://www.loudthinking.com/arc/2006_09.html