I currently took the Zend Certified Engineer exam for PHP 5.3 a few hours ago... and passed it!
I am pretty happy about the result as I have been studying for this certification for 2 weeks and did a 2 day all-day review 2 days before taking it so all we be fresh.
About the exam, there is a non-disclosure that I am not suppose to share anything about the exam but I can give you an idea about it in general.
The exam was pretty challenging. I actually thought im going to fail it at the end! I think in order to pass, you really need to be familiar with PHP and be coding with it for some years, have pretty good analytical skills and good attention to detail.
Here are some good tips that I can think of while I was studying for it:
1. You need to know the PHP functions, array, strings and so on that you will see in the study guide and php.net! I would suggest that while you are reviewing that you try each function once by actually writing it in PHP and running it! You'll get familiar easier that way...for me that is.
2. Review SPL, XML (SimpleXML and DOM as you will see in the study guide) and the new additions in PHP 5.3 like namespaces and static bindings! I would suggest writing some sample scripts again to familiarize. Know its quirks! When I was reviewing I try to find out what coding styles will work and what will not and why/how does it generate that, whats valid and whats not.
3. Do some practice test, actually a lot of practice test! You can try purchasing exam vouchers in zend.com.
4. Read the official study guide from Zend. I went to every link reference that was suggested there and read what I think was important. I also made sure that I know and can answer correctly all of the test questions in that study guide. If you are unfamiliar of something, go to PHP.net and review it!
So in summary...
Does it make you a good coder... No, everyone of us codes differently and have our own styles and by passing the ZCE doesn't really certify that you write clean, understandable and conforming codes. Wish it does though.
Does it certify that you know the PHP Language ... Yes, unless you are a pretty darn good guesser, the questions require that you are really familiar with the language and its "quirks".
Does it prove that you have good analytical skills... Somewhat, you need to have good analytical problem solving skills which requires you to analyze the given codes as stated in the study guide (Emphasis Analysis vs Memorization).
Is it worth it... For me, yes, because the feeling of satisfaction that you achieved something feels good :)