I like DVD commentary tracks, they give an insight into what the people behind the scenes are like, and more importantly into the creative process. If it weren't for DVD commentary tracks I wouldn't know half as much as I do about film.
And I think they work for comics too, at least in general (haven't read WSPoUG yet); Arkham Asylum (the book, not the game) was great on its own, but then I read Grant Morrison's annotation/commentary thing, and it opened up new layers of meaning. And the Calvin & Hobbes 10th anniversary book pretty much speaks for its own merits.
ADDENDUM: This just popped into my head: Would anyone have ever thought of DVD commentary tracks if it weren't for MST3K? Or is sitting down and talking about a movie while watching it such a universal experience that it would have happened anyway? But by that logic, MST3K itself is some kind of destined thing, a Platonic ideal made manifest on the physical plane, which waited until the technology existed to make it real. Like the flying car, or cold fusion. Or toothbrushes. I'm okay with this view, actually.
What if there was some kind of pre-motion picture version of MST that has been lost to history? Like, a troupe putting on a production of Titus Andronicus, but in the front row is three guys making witty remarks about the play, and they are who the audience has really paid to see. That would rule. In the absence of evidence to the contrary, I'm going to believe that this happened.