I'll add a few cents of my own ;-)
I've used both - Perl is a more mature, very stable language - I like Perl a lot - for everything. Perl as DBI for database integration, which is excellent and rock solid - as of 1 1/2 years ago(I haven't used PHP in the last year and a half), PHP didn't have any "standard" database independent layer, so I chose to write my own, which was a fair amount of work.
But, PHP is very nice for web development! It is very fast, and I really liked the ability to mix code in with the HTML. And, you get a lot of nice tools for web development for free with PHP - the big one in my mind is session management. Perl has the Apache::Session module, but that's a separate module that you have to download and install.
Perl has excellent documentation, which as of 1 1/2 years ago, was quite a bit better than PHP's, IMHO.
Those are just some random thoughts - my experience with PHP was a positive one - I wouldn't hesitate to use it again for web development given the chance. But I also love Perl, so take your pick.
HTH. Hardy Merrill