Finally, after an experience of 4 years and hours of studying, I am a Zend Certified Engineer today. The exam is not as tough as I expected, at the same time its not an easy one. For studying, I would recommend php|architect ZCE study guide. It covers all the topics, But the one book that helped me a in detail and advanced study in PHP5 unleashed from the author ‘John Coggeshall’. He has covered the more details that any book on PHP on the planet may have covered.
Its worth taking this exam as I learnt a lot new things about PHP now.
Find me on Zend yellow pages @ http://www.zend.com/en/store/education/certification/yellow-pages.php#show-ClientCandidateID=ZEND012882