In response to a question he got about the choice of a laguage (PHP or Python) for a web application, Terry Chay has responded pretty simply:

I still need to write another article on Python, but the short answer is I think if it’s web, PHP is probably the better choice.

He does have a few other things to consider that might make the choice swing the other way though - budgetary concerns that might push you to something a bit cheaper (like Python and the Google App Engine) or if you'd want to keep things the same throughout the whole application and is more flexible than just a web language.

PHP may be the best web language out there. But it certainly isn’t the only one. It’s one approach, one that stresses configuration over convention, stupidity over smarts, practicality over elegance.