Well, in dealing with PHP versus Perl for CGI, there is always that one BIG issue called security. Generally, the way the latest builds of PHP have gone, you have less control over security dealing with PHP than you do with Perl on systems where you don't have access to configure the php module/executable. If you did have such accesses, then you wouldn't normally have much of a problem getting the Perl modules in that you need. PHP is quick, and is coming along fine in a timeline relational way. Perl is much more mature than PHP.. But PHP is almost purely web based, and there are much more reasons to use Perl than for the web. If you can get a host that deals well with securing PHP, then I'd say that, if you're comfortable with the language (many ppl like it cause it's more strict than Perl's freeform on a syntax level, which can lead to overload when there's several thousand ways to do something in Perl) then PHP can be a better choice. I have started playing with PHP and it does tend to be easier to develop the front end, but right now there are several security issues with the default config of PHP that many hosts tend to use. Aside from the security tho, PHP is nice on a front end level, using Perl for several backend tasks. The two languages can live in harmony and can compliment each other well... But I still tend to lean towards Perl for more hardcore tasks. No, I'm not a professional developer, but that's my tendency so far, and I don't see it changing unless I'm paid to work with PHP..
anyway.. my 2 pence..
-Syn0

Update: Oh, damn... I forgot the most important reason why Perl kicks ass all over PHP.. thanks to John's post, I remebered.. there is no PHP community in comparison to Perl.. the Perl community is one of the most sharing, strong prescences I've ever seen. It continues to inspire my fierce loyalty and I just had to mention that as well.. PHP has a ways to go for this kind of thing.