The biggest problem with exit interviews is that they’re too little, too late. I had an exit interview recently (since I accepted an offer to go elsewhere), and there wasn’t anything wrong with the questions–it was just that nothing could be done about any of the concerns I raised.
The second major problem with exit interviews is that they focus too narrowly. All the feedback from exit interviews comes from people who’ve decided to leave. Assuming a company has had relatively low turnover for awhile, the feedback could be leaving out information from as much as 90% of its workforce.
If a company is serious about employee retention, they need to get feedback from as much of their workforce as possible on a regular basis. In my exit interview, I got questions about benefits, commute, holidays, and other issues. Regular, anonymous surveys on those issues would probably reveal a lot of useful information about ways benefits could be improved. Gathering this kind of information regularly will mean that at least some (if not most) of the answers you get will be from people who still have a stake in the company’s future.