A while back I passed the Oracle Certified Programmer for the Java 2 Platform SE 6.0 (formerly SCJP 6) exam and thought that overall it was a challenging exam. The questions required you to have a good handle on the language and framework but you really needed to concentrate on each question and look for small details that would result in the correct answer.
As for content, if you follow the SCJP Sun Certified Programmer for Java 6 Study Guide by Katherine Sierra and Bert Bates book that will give you a good start on the content. I also recommend a mock test, such as the one offered by whizlabs. I used this and found it to be helpful to familiarize myself with the exam format. Javaranch is also a good resource.
SCJP 6 Exam Simulator http://www.whizlabs.com/