DVDs and their supplemental materials can be wonderful things, offering insights into a particular movie or television show, providing the chance to catch up with some of the talent involved, giving background on how what you're watching came into existence.
But they need to be put together with some care. It's not enough to simply throw some people into a room and record what they have to say, or stick a camera in the midst of a cast reunion. Do that, and most of what you'll hear are exclamations of how great everyone looks or how much fun they had in making the film.
It's almost always best to recruit a third party, someone not intimately involved with the project, who can offer perspective, who can ask the right questions, who can steer the discussion away from the mundane and extract information that's not only nostalgic, but informative.
There are exceptions, of course: Martin Scorsese, for instance, all by himself, could make an episode of Romper Room seem exciting. When the commentary track for Stuart Gordon's Re-Animator was released, it captured cast members having a good time in each other's company while offering up interesting tidbits and perspective.
But please, don't simply offer actors or directors the chance to talk, and think that's enough. That's what happened when the first season of I Dream of Jeannie was released on DVD, and the end result was 24 minutes of Barbara Eden, Larry Hagman and Bill Daily complimenting each other on how funny they were. Even a trifling '60s sitcom deserves better than that.