PHP is certainly powerful. It has much of the functionality of Perl. While both languages overlap somewhat, I think PHP has more of a niche in web applications.
PHP is good for dynamic websites that need to be deployed quickly. With a little regex work and perl script or two you can even convert existing sites to PHP. Howerver, I think on larger deployments PHP pages can become harder to manage (templating may help this).
Perl is still the swiss army knife of scripting languages. Whether your site is big or small Perl will easily handle you requirements.
Neil Watson
watson-wilson.ca
