I took this test a few weeks ago and thought I would offer some pointers on how to prepare for this test.
I've been doing Silverlight development for over a year full time now, so that obviously helped out a lot. There are some questions about using a ViewModel and setting the right DataContext. So if you've only done code behind, you will be at a disadvantage.
A great resource is the Practice Testing Software from Self Exam Engine. I spent around $100 on this software but it was worth it. Many of the questions you will study are exactly the same on the real test. I would say at least 50% of the questions I had seen and studied.
The book Silverlight 4 In Action is great. And I used that as a study tool too. I would look at certain parts of the book where I didn't have that much experience, and take notes. Topics such as setting up an OOB and Printing will come up on the test.
silverlightshow.net has a great series on preparing for the exam. I went through each of their articles and looked at the links they provided. I would focus on the topics I hadn't worked with very much, or at all.
Using these resources I was able to finish the exam in about 75 minutes and score a 90%. They give you almost 3 hours, so you'll have plenty of time.
Silverlight is a big topic with many parts to learn. Even if you've used Silverlight quite a bit in your daily job, there will be topics on the test that you will not know the answer to. So study up, and you'll do fine.