After having recently taken the PHP5 Zend Certified Engineer exam, Mike Bernat decided to shares some experiences about the time he spent preparing and his opinions on the test.
I decided that I wanted to take the test about 2 1/2 months ago. The first thing I did was visit the site and learn more about the exam itself. I discovered it covers almost every facet of the language and its use. [...] It's been mentioned before and I agree that none of these resources [websites, books, etc] alone are enough to make you feel confident going into the test. Rather, a combination of each resource should be taken advantage of to feel fully prepared.
He specifically mentions two books - the official Zend guide and the php|architect study guide - as well as some of the online testing he went through.
On the real test, he warns those looking to task it in the future of a few things - the trick questions, code blocks and some of the tougher subjects to watch out for.