I don't get why they update their site so late, but it seems it's standard for conferences to provide the information as late as possible.
I wanted to know the details so contacted them and asked for details. The confirmed date is saturday the 14th of June with a 'pre-conference' tutorial day on the 13th, where workshops about Zend Framework, PHP Advanced, Symfony and possibly other subjects will be held.
Hope to see you there!
http://phpconference.nl/
* update 27-02-2008 *
According to a blog post by Joni Overbosch, Derick Rethans will speak at the dutch PHP conference 2008. Good news for me, I can now finally let the book PHP Power Programming (pdf version here) to be signed!
* update 21-02-2008 *
The new website is up and running. Check http://phpconference.nl for information, speakers and schedule