Back in July I popped down to London with a colleague, Stephen, to take the EPiServer CMS certification test which we both passed qualifying twentysix as a Premium Solutions Partner.
Today, our certificates arrived and I'm proud to say I am EPiServer Certified Developer #712 and Stephen is ECD #713:

I've been using EPiServer for nearly two years now, having taken the basic developer training at the end of January 2009 and in that time I've worked on some large and exciting sites but the prospect of the certification, the possiblity of failing it and the peer pressure that comes with was quite daunting. In the two years I've created two or three sites which I would call a Standard build, comprising a single web and/or database server, no mirroring, no custom page providers no use of add-ons or 3rd party integrations.
I've also created a few sites which weren't standard, integrating with bespoke and off-the-shelf 3rd party systems. Mirrored and load-balanced deployments. Deployments which use SQL Server clusters and most recently, I've written a Page Provider to integrate nopCommerce into a CMS 6 site.
On top of all this I've done the usual amount of hacking around in the SDK, re-written and extended a few of the EPiServer controls to add additional functionality (Such as Alternating Item Templates in the PageList and NewsList control [post to follow]).
Tips for passing the exam
It was quite hard to find a good exam guide for the certification and we found a lot of blog posts saying how hard the test was which I don't entirely agree with. It wasn't a walk in the park but it was fairly straight forward.
Read the Developers Guide
I can't link you straight to it because of the funky JavaScript navigation (you can find it easily from the SDK documentation).The developer guide is a gold mine!
If there are areas EPiServer you haven't worked with before but you have a decent understanding of the core functionality, you can pick up a lot from these documents. A few of the questions I knew instantly as I'd re-read and revised all the articles in this section, some of these questions were on functionality I'd never used.

Read the Tech Notes
Same goes for the Tech Notes as does the Developer Guide, read them all. The're not as long or detailed as the articles in the Dev Guide but they helped me answer a few questions.
Re-read the editor and administrator manuals
When someone is asking how to achieve something in the CMS from a user point of view, I sometimes find I'm not the best person to ask, while I do Develop EPiServer sites I don't spend hours in the Editor working with trees of pages, workflows and all the other gubbinz that make up the CMS. To this end, I'm glad I gave the Editor Manual and the Administrator Manual another read.
Read the internet
I'm not suggesting you read all of the internet, but if you're reading this, the chances are you've already Googled for tips on passing the exam. Here are some that we found:
Good luck!