For me, one of the most exciting things that we have in PHP 5.4 is its built in web server. It makes being able to jump in the deep end with new ideas much easier and avoids the tedious work in setting up and needing apache to run before you have code to deploy. I have been playing around with the Silex framework in the last few weeks to build a prototype of a REST API that I have been thinking about. This is how I got going with Silex once I had PHP 5.4 installed.
php -S localhost:8080
Create an index.php in the current directory (there’s an example app on the Silex home page). That’s it. Go play. :)