The only reason they can use PHP in the front end is because they have a lot of different backend and frontend services to compensate for it speed-wise. Facebook uses HipHop, backend services written with C/Java/etc(?), and lots of interesting frontend JavaScript stuff to speed up page loads. Wikipedia has literally hundreds of Squid servers to cache requests, so most visitors never touch code that was just generated with PHP. Needless to say, this would be unlikely to be possibly using PHP Fog. (This comment sort of turned into a PHP is slow argument, oops. My point should still come across though)