I only can write something about Sun Java-related certificates because I'm happy owner of three of them (SCJP, SCJD and SCWCD - and preparing for SCEA). Do professional and experienced developers need such papers? Aren't they useless and worthless?
Many people don't believe in certificates. They claim that they do not give any value and are only PAPER. The only (is it really only?) thing they can help you is to find better job. They also claim that certificates' value is just bringing satisfaction to their owners - satisfaction that you passed difficult and worthless exam.
I absolutely don't agree with such opinions. First of all because developers tend to take their knowledge for granted. We think that our job is easy because it's easy for us. We forget that some of us worked for current knowledge state since early childhood (I started coding when I was 10 ;).
Certificates are almost as important as our university diplomas. I would risk saying that they are even more important because they prove that we do something with our knowledge after leaving university. But the most important factor that should convince everybody to try and take some exams is that they are really valuable (maybe except for SCJP). I learned a lot of useful stuff during preparation for my exams. And what is even more important I can easily apply what I learned in my daily job.
And YES, they help you very very much if you want to change your job!
If you can learn something useful that can help your daily job, if you want to have some fun and become more competent and competitive developer, why not give it a try? I highly recommend every developer who can spare some time to take Sun Java certificates - they are very useful and worth your effort!