When I was back in the states this summer I picked up two DVDs, Miller's Crossing (one of my favorite movies), and Fight Club (because it was a cool movie and had a lot of features). So I watched it once through without any commentary, then watched it with each subsequent commentary (4 total), at different sittings, starting with David Fincher's commentary. This led me to read the highly original and entertaining book by Chuck Palahnik, whom, incidentally, I didn't know was from Portland Oregon. As we speak, he has three novels on the top 20 bestsellers list.
The commentary by Edward Norton, David Fincher, Brad Pitt, and Helena Bonham Carter was equally interesting. For example, there's a line in the book where Marla (Carter) tells jack that she wants to have his abortion, and the studious wouldn't let it stay, so Fincher came up with "I haven't been fucked like that since grade school."
After seeing the dailies, the studio wanted it changed back. Carter who is from England didn't catch the significance of "primary" grade school at first.
I also liked the Writer's commentary by Palahnik and screenwriter Jim Uhls. Palahniuk in particular was very forthcoming about where he got ideas for a lot of the material. Apparently he had gotten into a fight camping one weekend over loud music at a campground and had some severe bruises on his face and he realized that people ignored it and wouldn't look him in the face at work, it made them uncomfortable. Some of the support group material came from when he volunteered as a driver for terminally ill people. I found it funny to see Uhls take credit for making the support groups names, considering in the previous commentary Norton explained that he took them from Planet of the Apes (Cornelius and Rupert), and some other source that escapes me now.
By the time the fourth commentary came around, the Technical Commentary, I was a little burned out and didn't really care so much about where they found Brad's leather jacket or about lighting decisions. But all in all, a very in dept and interesting look at a ground breaking film. I hope Fincher can make more cool movies like this, since I was very disappointed by Panic Room.