PHP is amateurville. I can’t imagine a first rate pro website being written in it.
You just need to know it to maintain or update the old ones. Same with Perl.
PHP is used on a vast majority of web sites (that require server side programming). I remember reading recently from a Alexa ranking that the of the top million web sites, nearly 80% use PHP.
Check out the Laravel framework. It will guarantee its popularity (and growth) of PHP for the foreseeable future.
Every language has it's quirks.
It's the poor workman who blames his tools. ;^})
Yahoo!, Facebook and Wikipedia are just three sites using PHP. Then, there's LinkedIn and WordPress.com.
There are a number of MVC frameworks supporting PHP including CakePHP and CodeIgniter.