The good news is PHP looks a lot like Perl, the bad news is PHP looks a lot like Perl.
It's a snap to learn if you know Perl. You won't even need to read any books or anything, you can work with it right now. I do find it annoying that they're so similar you start to get things messed up in your head. Things start blending and you can get confused. The major pitfal is the lack of "use strict". (judging from a lot of questions asked here on PM people aren't using strict, but anyways...)
I don't hang out anywhere for PHP, you don't really need to. You'll find everything you need by Google it when you need it. Everything will be on php.net, and anything else on stackoverflow.
As much as I love Perl and get annoyed with PHP, after working with it a while I do to admit it PHP has some nice features that make basic web development pretty quick. Having the webserver keep track of session data is really nice, and it plays well with mysql.