Sure, Facebook and Wikipedia are built on PHP, and they serve to very many happy users. But are the developers very happy? PHP works, but for most cases, there are better solutions, and we should strive for better. Just because some sites were successful in doing it doesn't mean 'PHP sucks' isn't a valid argument.
I'm fairly happy as a PHP developer. It pay's the bills... there are times when I am presented with a mess which makes me want to shoot myself in the face. However I am sure such messes can easily be created in other languages. PHP has a history of Spaghetti code and when I was learning it mashing mysql, php and html into the same file was 'the way to do it'.
Today though PHP development revolves much more about OOP frameworks like Symfony and a good application structure.
The thing that bugs me most is inconsistency in core functions. Is it functionname or function_name. Is it ($needle, $haystack) or ($haystack, $needle). However, it is a minor annoyance negated by a decent IDE.
