I prepared mostly with the K&B book, taking the practice quizzes on the CD, and a couple of mock tests on the new Java 5 features at javabeat.net. I went into this thing pretty nervous, afraid that I was going to choke, but am glad I passed with a decent score! I was mostly worried about forgetting API calls, the new drag & drop type questions, and generics.
I was surprised though that being an upgrade test, there weren't more questions specific on the new language features of 5.0. I found it covered pretty much all of the objectives evenly, so I'm glad I didn't focus strictly on the new language features and went through the entire K&B book.
My tips: * Get the K&B book. * Take as many practice tests/quizzes before the real exam. * Give yourself enough time to study, at least 2 solid weeks. * Save for last the drag&drop questions if you're spending too much time on them. * Read Javaranch.com!