The Level 1 exam isn't too bad. I just took it.
If you brush up from the Apple Pro Training Series FCP book, you'll be fine.
Just read the questions on the test carefully.
I don't think it's a bad thing at all to be certified, but good work is what will get you the most jobs. If you're looking to get hired by a production house, then having "Final Cut Pro Certified" on your resume and business card can't hurt.
The Weynand book is all you need. That's the book that certified courses are taught from.
If you take the Level 2 exam, you'll need to familiarize yourself with the material in the "Final Cut Pro: Advanced Editing and Finishing Techniques", also a part of the Apple Pro Training series. That book was assembled by Digital Film Tree.