Anyone who’s really thought about MySQL relative to other database engines, in particular PostgreSQL, knows it’s pretty much “The Thing that Should not Be”.
Personally think PHP is also a disruptive technology.
Anyone who knows PHP well can probably tell a thing or two about monsters in the closet, and that’s before you open up the debate to others.
But when it comes to ease of use, it’s extremely hard to beat PHP. Not only is it a great language for beginners, there’s a strong business case for a technology that’s focused on a solving small set of problems and is as easy to deploy as a PHP script (Java take note). PHP attracts developers who “should know better”.
In these days of J2EE and .NET, by all rights, PHP should be condemned to obscurity. Instead it continues to grow and, with PHP5 almost there, seems to be attracting ever more “Enterprise” attention.
Why? The best arguments I’ve seen came up in Is PHP Ugly? by Jeff and Markus: “worse is better”.