No one at Facebook is under the impression that PHP is a particularly good language, but it does the job. What really matters are a libraries and abstractions that you'll actually be interacting with. At Facebook these are leagues ahead of any other PHP codebase I've seen.

You should read what Andrei Alexandrescu has to say about the language here: http://www.serversidemagazine.com/news/10-questions-with-fac...