So I'm back at IBM after a year of being a student. I spent the first couple of weeks easing myself in gently by doing a little more PHP opcode documentation, see here. I'm hoping we can move this into the manual.
Things have moved on a little whilst I was out getting educated. In October 07 the PHP runtime used in Project Zero (aka WebSphere sMash) was just running PHPBB. Now it's really looking much more capable, in addition to PHPBB it runs SugarCRM and more recently also WordPress and MediaWiki. I'll be interested to see how the team exploit the possibilities for close integration of Java and PHP code.