If you are looking for a job in Java technology, then the Sun's Java Certification adds a lot of value to your resume.
Especially, I think if you do not have any industry experience in Java technology, and you are looking for a job in Java, the certification will increase your chances many-fold. On the other hand, if you already have quite some experience in Java, then, probably getting a certificate would not matter too much.
It is hard to put dollar value on the Certification results, but on average, certified programmers get higher salary than non-certified programmers, everything else being the same.
Nevertheless, being a Java programmer myself, I think taking a formal certification exam will help you know a lot of nifty details of the java programming language and related technology. It will also help you with doing interviews. This is because in java job interviews, you get all sorts of odd questions that are not common java knowledge, but should be covered by the certificate preparation.
In today's tough job market, a certification from an established vendor like Sun can act as one more selling point In your resume. All else being equal, most employers will prefer a certified candidate. Certification alone does not guarantee a job. But it acts as a reassurance to a prospective employer that the candidate at least understands the basics of Java. The certification is especially useful if you are a new graduate or if you're looking for your first job in Java.
Perhaps even more useful than getting file certificate is the learning involved In preparing for the exam. The certification enforces discipline. Most people are too busy with their jobs to have time to stay up-to-date on the latest technologies. Preparing for certification helps bring focus and discipline, and lets you update your skills on a specific technology. The certification exams from Sun are Industry standard and well recognized in the industry.