PHP is just a rather nasty language. It's got a lot going for it, in terms of deploy-ability, scalability, existing libraries and code, and number of developers and designers who are familiar with it, but it's also got a horribly inconsistent standard library, poorly implemented seemingly Java-inspired objects, and a vast majority of the existing code is poorly written.

There are some impressive PHP projects out there, with pretty clean code (I've been pleased by the quality of code in Dokuwiki and Flyspray, for example), and you can't beat PHP with a stick for availability--you can deploy a PHP app on the cheapest Dreamhost account and expect it to work just fine. That cannot be said of RoR, Django, or Catalyst applications (and don't even think about Lisp or Haskell or Erlang in that context).