I still stick to my theory that social engineering is a fancy term for lying. And I still don't consider lying a form of hacking, it's a form of manipulation.
.Its not lying man! Its charming or tricking people!

Social engineering is the single most effective security penetration technique of all. You can put a computer inside a sealed room with 10 foot thick concrete walls, but if any employee who knows the login sequence is chatty, lonely, or otherwise pliable, 50 foot walls won't secure the system. Security is made up of a chain of connected elements : firewalls,passwords,shredders,alarm systems, secure rooms,etc...
But the old adage applies: the security chain is only as strong as its weakest link. And all too often that weak link is a person.