Certified ethical hacker is an examination that certifies you as an Ethical Hacker. Ethical Hacker is a person who do penetration testing(Hack) a system to find the flows in the system. Note that this is a legal thing. A company will ask an Ethical Hacker(Also know as White hat hacker) to hack their system and provide information and consultancy on the security of their IT system. I have looked at this exam, and also gone through some parts of the book. It's really interesting but I do not think anyone would become a hacker after doing this exam. Hacking is not taught here, but the book do provide information on some useful tools and stuff.
But CEH is not the best certification for security specialists. The best one is CISSP. This is considered the highest paid IT certification in the world to the best of my knowledge. Since there aren't many security jobs in SL people dont usually do the certification like they go for CCNA or MCSE. I think i have only met one person who has the CEH certification.