I wrote Tumblr, Instapaper, and Second Crack in PHP. I continue to use it because I know it extremely well, it’s very easy to use and deploy, and it’s nearly maintenance-free on servers.
When you’re a programmer forced to also be your own sysadmin, that’s very attractive.
I like this article because I myself am a PHP addict. I’ve worked with the other languages, but for all its many flaws, I keep coming back to PHP for most projects, and don’t see that changing anytime soon.