Well, it just so happens that if you add "?=PHPE9568F36-D428-11d2-A769-00AA001ACF42" to the end of any URL that is a PHP page you will see a funny little picture of a dog. Try it right now with any URL on digg!

From: http://www.digg.com/programming/PHP_Easter_Egg_(Works_On_Digg_)
by: ptcfast2

They also have the logos and credits...

53 #define PHP_LOGO_GUID "PHPE9568F34-D428-11d2-A769-00AA001ACF42"
54 #define PHP_EGG_LOGO_GUID "PHPE9568F36-D428-11d2-A769-00AA001ACF42"
55 #define ZEND_LOGO_GUID "PHPE9568F35-D428-11d2-A769-00AA001ACF42"
56 #define PHP_CREDITS_GUID "PHPB8B5F2A0-3C92-11d3-A3A9-4C7B08C10000"