Justin Silverton has posted a comparison between PHP and Perl, with the first part coming more from the PHP side comparing it to Perl and the second the opposite.
He starts off with some of the differences between the two langauges, including that PHP was made for the web, Perl was not and that PHP scripts take less overhead for the web server to run that Perl scripts as CGIs. There are also four larger topics that he looks at:
- PHP has separate functions for case insensitive operations
- PHP has inconsistent function naming
- PHP has no lexical scope
- PHP has too many functions in the main namespace
All but the top item (that one could be argued either way) are reasons that a Perl user might cite against using PHP. For each of the items, there's a bit of description following to give you a better idea where they're coming from.