Certifications are most probably not worth it. Most employers look more at what you did before.That said, studying for certifications is worth it and will help you pick up the core basics. Preparing for it might give you more confidence when facing interviews since you will have sealed the basics by then.
The SCJP is not really a highly regarded certification amongst Java developers, but big employers love it. Some of the books to prepare for it are thorough and give you many opportunities to pick up nitty-gritties of the language - some known that you revisit, some unknown which might be really important.
I have stumbled across a lot of blog posts where programmers rave about something they just discovered in the language, but which are known to most people who leafed through the certification books.