For site like Flickr, Wikipedia, and Facebook - all of whom deal with enormous availability problems - to have stuck with PHP, well, that means something profound. While previously I respected PHP programmers, I always felt that they must not understand much about actual computer science. They were stuck in a procedural world, and a glimpse of what "more advanced" languages could show them would "enlighten" them.
He suggests that PHP scripts, especially the "large libraries" some developers create do some very routine tasks that could be accomplished much simpler. He points out, though, that PHP does have something going for it and that, despite a difference in functionality offered, Lisp could learn something from PHP.