Tim Bray has a nice post that succinctly describes the situation with PHP in 2008 -- why it's still popular, but its growth continues to slow.
I think that the various pluses and minuses could be reduced even more by simply thinking of PHP as the McDonald's of programming languages.
PHP, like McDonald's, is really, really convenient, -- it's pretty much already installed everywhere you go. Deployment, like eating at Mickey Dee's, is a breeze.
And maybe I'll be totally ostracized for saying it, but I don't particularly mind using PHP to set up a quickie Web site with some simple templating. It's dead simple, and I know stuff will just work.
Like the food at McDonald's, using PHP isn't that bad every once in a while -- but I wouldn't want to eat it every day. And I'm pretty sure a steady diet of it will kill you.