My previous employer had exit interviews. In general, they are trying to find the reasons that you are leaving and improve employee retention in the future.
One important advice would be to really say nothing :) Just repeat that you really like your soon-to-be former workplace but have to "move on", or maybe say you got a very good offer that you could not refuse.
If they had any interest in changing things, they would have asked you about it and done it before you decided to leave.
So the best policy is just to say that while you've decided it's time to move on, you had a great time working at XYZ Corp and will always remember it with fondness.
I never forgot the time the company I worked for invited about 20 of us into a room to tell us we were being laid off. The president of the company was in a speech about how he hated to let us go but blah, blah, blah, when one of the guys in the "about to be let go group" said "Can you speed this up, I've got a job interview to go to". That guy got a huge round of applause.
I don't know if I 100% with some of the other posters... why not be honest (but diplomatic), so that future employees can have it a little better?
Update
Some topics for developers:
Did your employer not let you play with the latest toys (or at least toys from this millennium?) Lots of companies have a "if its not broke don't fix it" attitude, which is fine... but programmers tend to love the latest and the greatest, so they need to accommodate that somehow.
Did your employer provide you with an appropriate work environment? Was it unreasonably noisy? Did they provide you with adequate equipment?
Were you constantly micromanaged?
Were you constantly given unreasonable expectations?
Were you paid what the market bears?
Were you constantly working well over 40 hours a week? Was it without compensation?
(Related to the last question) did you have insufficient down time? We are not factory workers, we need some percentage of the day or week to have freedom to explore new technologies and strategies.
If you leave because you disagree with your manager or the company operates, this is your opportunity to provide feedback. But don't burn bridges, there is a high likelihood they may want you back at some point in the future.
I have jumped ship a few times in my career. Here are my answers to your questions of exit interviews:
Not every company I have worked with has done exit interviews. When they did, they were a last minute plea to see if they could change my mind.
Software dev topics: If you are leaving they will want to know if it was because of the type of work- which for software developers means what paradigm and languages. This may be to find out if they could entice you to stay if your work were to change or just to know that maybe everyone is leaving the company because hey, they hate cobol (just using as an example).
Employer perspective: For you to leave, the company will likely think it is something they did that forced your hand. They will want to get an accurate account for why you left so they can predict this in the future- which can have an affect on what salary and raises other employees receive. Example: they may not make as much of an effort to keep someone like you next time if they think it will just backfire again- Or, maybe they can get to someone sooner if they see the same signs, Or- maybe they can change hiring practices to have better retention of quality people.
Positive impression: It depends on the company. Even if you leave on good terms, they may still resent you leaving if you were a valuable asset to the company. This also depends on the size of the company.
Another war story:
I worked in a company (Gandalf.ca) where my boss was great, but his boss was constantly breaking the chain of command to come down and harass me and the people who worked for me directly. When I left, I wrote HR a long letter with specifics about how bad this guy was as a manager, how much damage he was doing to our group, etc. I lavished praise on my direct manager, again with lots of specifics. A few months later, I found out that they fired the doucebag, which I was happy about, until I also found out that they fired the good manager. I felt kind of guilty about that.
I never heard of exit interviews in Germany. There's enough time to talk with each other, because there is a long notice period.
This is one of those situations where you have very little to gain. Tell them the things that are going wrong with the company and you're likely to be labeled as a bad egg (or chose your own metaphor). If It's amazing how much resistance people have to constructive criticism but i guess we are all human.
In the companies I've been in the interviews are generally done by HR, but i've been places where I had an exit interview with both my manager and HR.
I guess if you are genuinely leaving to go towards something (a genuine great opportunity) as opposed to going away from something (bad management, crazy overtime) then you might be able to provide some pointers. I think people and companies are more receptive to small incremental changes (we should work more closely with the QA team etc.) than they are to the really big issues.
As for performing the exit interviews. If you are a manager I think the key to getting good feedback is to already have a good relationship with the person. If there's no trust you're just going to get "it's time to move on." If there is real trust you might actually get the real deal on the situation. If it's HR... just read the form and check off your boxes.
My previous job exit interview was an informal lunch with managing director. He was mostly interested if there were any points to improve in the work atmosphere etc. Nice way to leave good impression on both sides anyways.
None of the answer cover what is, IMO, the most important. The guy is leaving, ok. But knowing why is not the only issue.
With this person going away, you may have the opportunity to have a feedback that can be given without pressure. It is time to find the answers you usually seek during ordinary assessments.
And if the guy was nice, it can be the opportunity to invite him to do something as a friend. Sometimes you cannot get out with people you like because your job just not allows it. Once the border is crossed, enjoy !
P.S : And sometimes it can just be good to say what a sucker he was. I know it's useless or counter productive, but it will make you feel good and may prevent you from setting on a psychoanalyst chair when you'll be 50.
OK, say you've just been dumped by your girlfriend.
Exit interviews are a bit like holding a gun to her head and asking her to honestly; no really, as honestly as possible, say what they think of you.
Exit interviews are, IME, usually an example of the numerous situations that arise in big companies that are completely and totally detached from reality.
On that basis, just speak in positive generalities and pour praise where you can.
It's too late! The time for asking the questions in an exit interview was 3 months to a year ago, when the information gleaned could have done some good and facilitated retooling the relationship to make it more profitable for the employee and the company.
Employees, don't say anything in an exit interview other than "Well, I don't really have anything to say about that." The only thing you can accomplish is to burn bridges. You might not care about burning bridges back to the institution, but you should, and worse, you can also burn bridges to people that you may have to deal with somewhere else some day.
Companies, if you really think the questions in an exit interview provide useful information ... then why aren't you asking them of all of your employees, now?
From a pure self interest point of view, your best bet is to give a warm and fuzzy (yet not necessarily brutally honest) account. Sugar coat why you are leaving, and dont' burn bridges.
Why? It's the best result for you - you personally gain nothing by really venting on what all the problems were, and stand a risk of killing opportunities in future when you come across the same people again (which you will eventually).
So go with the short, sweet, and shallow responses. Then get out and carry on with your life.
I'd like to attempt to answer this question myself. I'm in a kind of ambivalent situation: I'm a developer, but I am also a co-owner of a company. So I am very interested in understanding what drives developers away.
I can tell you that it is not easy job being a good employer. You have to consider so many things, and satisfying all your employees' needs is a very hard task under certain circumstances.
I am a little surprised that many answers picture a hostile relationship between companies and leaving employees. My experience is that (young) people who go away in many cases are looking for new challanges, maybe leaving for a job in a foreign country. This doesn't imply that the job at your company was a bad experience.
To people who contributed much to the company's success, I always try to tell that it was hard letting them go, I wish them all the best for their individual future.
Then, there are some practical aspects: there are some legal things to emphasize, e.g. a reminder for non-disclosure agreements, email-forwarding for some time, asking them if it was okay if they could be contacted for possible questions etc.
Another aspect is that exit interviews provide an opportunity to 'make peace' with disgruntled employees, who might otherwise leave with vengeful intentions.
What's useful is the resignation interview, rather than the exit interview. When someone tells you that they're off that's the point you need to start a dialogue:
The first point only works once or twice per person - threaten to go and renege once, but more than once and the company won't believe you're ever actually going to go.
The exit interview is then the end of this dialogue and to review how well the whole removal process was achieved.
I remember the last exit interview I went to. It started something like this:
HR person: "So why are you leaving?"
Me: "Why are you leaving?"
HR person: "Ah. Touche."