A few of you seem to have mistaken the definition of social engineering and some of you just missed the entire concept.
Well, this article from Security Focus is for you. Hopefuly this will help you with your understanding of social engineering. You can view the full article from here.

...Security is all about trust. Trust in protection and authenticity. Generally agreed upon as the weakest link in the security chain, the natural human willingness to accept someone at his or her word leaves many of us vulnerable to attack. Many experienced security experts emphasize this fact. No matter how many articles are published about network holes, patches, and firewalls, we can only reduce the threat so much... and then it’s up to Maggie in accounting or her friend, Will, dialing in from a remote site, to keep the corporate network secured.

Target and Attack
The basic goals of social engineering are the same as hacking in general: to gain unauthorized access to systems or information in order to commit fraud, network intrusion, industrial espionage, identity theft, or simply to disrupt the system or network. Typical targets include telephone companies and answering services, big-name corporations and financial institutions, military and government agencies, and hospitals. The Internet boom had its share of industrial engineering attacks in start-ups as well, but attacks generally focus on larger entities.

Finding good, real-life examples of social engineering attacks is difficult. Target organizations either do not want to admit that they have been victimized (after all, to admit a fundamental security breach is not only embarrassing, it may damaging to the organization’s reputation) and/or the attack was not well documented so that nobody is really sure whether there was a social engineering attack or not.

As for why organizations are targeted through social engineering – well, it’s often an easier way to gain illicit access than are many forms of technical hacking. Even for technical people, it’s often much simpler to just pick up the phone and ask someone for his password. And most often, that’s just what a hacker will do.

Social engineering attacks take place on two levels: the physical and the psychological. First, we'll focus on the physical setting for these attacks: the workplace, the phone, your trash, and even on-line. In the workplace, the hacker can simply walk in the door, like in the movies, and pretend to be a maintenance worker or consultant who has access to the organization. Then the intruder struts through the office until he or she finds a few passwords lying around and emerges from the building with ample information to exploit the network from home later that night. Another technique to gain authentication information is to just stand there and watch an oblivious employee type in his password.

Social Engineering by Phone
The most prevalent type of social engineering attack is conducted by phone. A hacker will call up and imitate someone in a position of authority or relevance and gradually pull information out of the user. Help desks are particularly prone to this type of attack. Hackers are able to pretend they are calling from inside the corporation by playing tricks on the PBX or the company operator, so caller-ID is not always the best defense...
They’ll call you in the middle of the night: "Have you been calling Egypt for the last six hours?" "No." And they’ll say, ‘well, we have a call that’s actually active right now, it’s on your calling card and it’s to Egypt and as a matter of fact, you’ve got about $2,000 worth of charges from somebody using your card. You’re responsible for the $2,000, you have to pay that...’ They’ll say, ‘I’m putting my job on the line by getting rid of this $2,000 charge for you. But you need to read off that AT&T card number and PIN and then I’ll get rid of the charge for you.’ People fall for it.” -Computer Security Institute Help desks are particularly vulnerable because they are in place specifically to help, a fact that may be exploited by people who are trying to gain illicit information. Help desk employees are trained to be friendly and give out information, so this is a gold mine for social engineering. Most help desk employees are minimally educated in the area of security and get paid peanuts, so they tend to just answer questions and go on to the next phone call. This can create a huge security hole.

Dumpster Diving
Dumpster diving, also known as trashing, is another popular method of social engineering. A huge amount of information can be collected through company dumpsters. The LAN Times listed the following items as potential security leaks in our trash: “company phone books, organizational charts, memos, company policy manuals, calendars of meetings, events and vacations, system manuals, printouts of sensitive data or login names and passwords, printouts of source code, disks and tapes, company letterhead and memo forms, and outdated hardware.”

These sources can provide a rich vein of information for the hacker. Phone books can give the hackers names and numbers of people to target and impersonate. Organizational charts contain information about people who are in positions of authority within the organization. Memos provide small tidbits of useful information for creating authenticity. Policy manuals show hackers how secure (or insecure) the company really is. Calendars are great – they may tell attackers which employees are out of town at a particular time. System manuals, sensitive data, and other sources of technical information may give hackers the exact keys they need to unlock the network. Finally, outdated hardware, particularly hard drives, can be restored to provide all sorts of useful information.

On-Line Social Engineering
The Internet is fertile ground for social engineers looking to harvest passwords. The primary weakness is that many users often repeat the use of one simple password on every account: Yahoo, Travelocity, Gap.com, whatever. So once the hacker has one password, he or she can probably get into multiple accounts. One way in which hackers have been known to obtain this kind of password is through an on-line form: they can send out some sort of sweepstakes information and ask the user to put in a name (including e-mail address – that way, she might even get that person’s corporate account password as well) and password. These forms can be sent by e-mail or through US Mail. US Mail provides a better appearance that the sweepstakes might be a legitimate enterprise.

Another way hackers may obtain information on-line is by pretending to be the network administrator, sending e-mail through the network and asking for a user’s password. This type of social engineering attack doesn’t generally work, because users are generally more aware of hackers when online, but it is something of which to take note. Furthermore, pop-up windows can be installed by hackers to look like part of the network and request that the user reenter his username and password to fix some sort of problem. At this point in time, most users should know not to send passwords in clear text (if at all), but it never hurts to have an occasional reminder of this simple security measure from the System Administrator. Even better, sys admins might want to warn their users against disclosing their passwords in any fashion other than a face-to-face conversation with a staff member who is known to be authorized and trusted.

The hackers themselves teach social engineering from a psychological point-of-view, emphasizing how to create the perfect psychological environment for the attack. Basic methods of persuasion include: impersonation, ingratiation, conformity, diffusion of responsibility, and plain old friendliness. Regardless of the method used, the main objective is to convince the person disclosing the information that the social engineer is in fact a person that they can trust with that sensitive information. The other important key is to never ask for too much information at a time, but to ask for a little from each person in order to maintain the appearance of a comfortable relationship.

Reverse Social Engineering
A final, more advanced method of gaining illicit information is known as “reverse social engineering”. This is when the hacker creates a persona that appears to be in a position of authority so that employees will ask him for information, rather than the other way around. If researched, planned and executed well, reverse social engineering attacks may offer the hacker an even better chance of obtaining valuable data from the employees; however, this requires a great deal of preparation, research, and pre-hacking to pull off.

Hopefuly this will help you with your understanding of social engineering..