Well...PHP has more built-in functions and less use of modules. It doesn't have those handy Perl input / output variables, and it does let you embed code in your page. The two languages are actually quite different, aside from the core structure and functionality that all programming languages seem to share, and in my opinion at least, they don't have much overlap. Perl is faster to code in, and easier to write complicated algorithms with, but it isn't suited as well to inserting small pieces of code throughout a page, and most remote hosting accounts don't have mod_perl, so PHP has a significant speed advantage for high-volume, low complexity tasks.

I use Perl for admin functions and data processing, and PHP for most of my web pages. I often generate PHP from Perl, or write a rough draft of something in Perl and then rewrite in PHP once I have a good lock on what I'm trying to do.