All questions are multiple choice. Moreover it's also indicated in a question itself how many answers it has, for example, "What is this class responsible for in Magento" - it means that the right answer will be only one, "Which two of the following you must do to achieve something" - and you should choose two answers.
I would recommend to start with the Fundamentals of Magento Development Video Course. It covers more than half topics from the Study guide. So before each chapter you can watch these videos and then start digging.
Students will leave the course understanding the Magento
architecture, MVC and data models, how to work with Magento modules,
and how to customize and extend Magento to ensure the best upgrade
path for the websites they extend
There is also a Study Group Moderator’s Kit you can get for a nominal fee. There is a set of exercises on different topics with code sample answers. This could help you not only to prepare for the certification, but also enrich your knowledge in general.
Since the Study Group Moderator's Kit isn't available anywhere, Vinai Kopp made an excellent, free resource: Grokking Magento: Book 1 - Magento Basics & Request Flow. This is an in-depth ebook on the study group material.
At BelVG we have a certification dedicated category in our blog. At the moment it covers only the first chapters, but we're working on it.
Magestore also has a lot of articles.
But the real way to prepare for exam is: all questions in certification guide have the following info:
These code references can be used as an entry point to find answers to
the questions above
Essentially it's a list of files/classes that need to be examined. There is no magic pill - you need to open all of them and check all main methods and analyze how they work. We spent 2-3 hours after work within 3 months to prepare for exam...
As additional info you can check, as mentioned here, Alan Storm articles, Knowledge Base, Magento Extension Developer’s Guide and Design Guide
Disclaimer: I passed exam in May of 2012, and it was based on Magento CE 1.5, from January of 2013 it's based on Magento CE 1.7 and I think that they should update Certification Guide.
Now, In 2016 it's based on Magento CE 1.9