I'm pretty certain people are paid to do the tracks aren't they? that's something to keep in mind, although I'm not certain of it, but how else would you guarantee participation?

I bought a dvd of Thelma and Louise, one of my all-time favorite movies, and it had a new commentary track with Susan, Geena, and screenwriter Callie Khouri. It started out very high energy at first (Geena sounded like she'd just consumed a cup of espresso and a whole bag of chocolate bars beforehand) and then gradually petered out and became boring. They kept talking about how the movie was received at the time and people were offended by women doing violent things in a movie (when men did similar things as a matter of course in action films); etc. But they got stuck on that loop and ran out of things to say. Bored, now.

If you can't talk about your own movie for the whole period, then forget it. Give me trailers or featurettes or something else instead. (The deluxe package for Moulin Rouge is awesome in that regard - hours worth of features. But Baz is on both commentary tracks and lady of mercy does he like to listen to himself talk.)