I am very intolerant of people who talk through movies. There are times for it, sure. If you and those watching the movie mutually decide this is a movie worthy of commenting through, or if you've seen the movie 700 times and it's just on for background noise.
The other main exception is when those involved with the film talk through the movie. I am of course referring to the commentary tracks offered on DVDs. For the most part, I enjoy listening to commentaries. I've even listened to commentaries on bad movies just to see how the filmmakers can justify what they did.
Commentaries themselves vary in quality. One of the worst I've heard was for Sky Captain where the filmmakers did not offer a whole lot of new information, but instead confirmed that most of the movie was digitally created. Sometimes the commentators get wrapped up in watching the production and don't say a whole lot. The commentaries for 24 are like this. Sometimes studios will counteract that by combining two or three commentaries into one track. Spider-Man's commentary was like this. And it was frustrating because I wanted to hear Sam Raimi talk, not the other track.
Here are some commentaries I recommend:
Star Trek Generations Ronald D. Moore and Brannon Braga tear apart the movie they wrote. They give great behind the scenes info on the politics of this movie. It's refreshing to hear them honestly admit to their mistakes. It doesn't make up for this movie, but it's good to know they realize where it went wrong.
Blade II Any commentary by Guillermo del Toro is awesome, but this was the first I heard. GDT is a genius and in the commentary for this movie, he shows how much thought and effort he puts into this sequel.
Firefly, pilot episode One of the funniest commentaries I have ever listened to, writer/director Joss Whedon and star Nathan Fillion deliver a laugh a minute in this commentary.
Buckaroo Banzai One of the weirdest commentaries I've listened to. Director W.D. Richter and writer Earl Mac Rauch are featured here. Except, Rauch delivers his commentary as though he were the "real" Reno Nevada, one of the characters in the movie. He talks about the movie as though it were based on real people. Very interesting approach, but a little bit confusing at first. For kicks, watch the movie with the text commentary on, too. That'll blow your mind.
Tastes Like Chicken, actor's commentary I made a little movie a few years ago and four of the actors got together to record a commentary. Very funny and very meaningful to me.