I am studying for the SCJP and half way through already I feel that I've learned a great deal about the nuances of the language and am really looking forward to diving into a project and not getting hung up on how to do basic things.
I feel though that a large part of the exam mainly tries to trick you with syntax gotchas that could be caught immediately by just typing code into whatever IDE you use. I do believe it's quite an objective way to tell that someone at least knows the language and will not need to get up to speed on learning it if hired.
I've found that many elite companies scoff at the SCJP. If you're applying to what may be considered a "top shelf" company perhaps you don't need it because you already have a C.S. degree from a respected university or have contributed to impressive projects in your experience.
Most mere mortals however could only benefit from the SCJP and what they learn through the process of preparing for it. Look at it as another leg up in our competitive field.
The SCJP 6 exam is also harder to pass than previous versions and this might be a response by Sun to raise the "prestige" of the certification.
I'd say go for it. I'm having fun and learning a ton.