Kevin Schroeder's Blog: Tapping millions of non-PHP PHP developers (manager's guide for Java to PHP)
I have had the benefit of being able to program in many different languages for many different environments over the years. Throughout that experience there are 2 languages that have risen to the top of my favorites list. PHP is one, obviously. But Java is the other. [...] To access all of the functionality in Java, there is a tradeoff with simplicity. To access all of the functionality for the web in Java, there is a massive tradeoff with simplicity.
He notes the cost of using one over the other (hint, PHP's usually cheaper) and, an interesting point, a story about a Java developer that took around two days to get comfortable with PHP. He lists a few things PHP offers that help including the low installation/initial code barrier, loose typing and the definition of functions without a return type.