It's funny. I remember when I first began going to art school I was real frustrated with my drawings because they were dead, stiff, and lifeless. Then I started noticing that the upper-classmen were taking reference pictures of each other, which they then based their drawings on. This caused a huge lightbulb to go off. Since then, and after reading everything I can get ahold of concerning Rockwell, I spend a considerable amount of time in the early stages of my work taking a ton of ref pictures and to doing as much research as time permits. The more time I spend getting the pose just right, and referencing the environment, the story-telling, lighting, composition, color, etc....the better the piece always turns out. It's just become part of the process now, one in which I enjoy, because it is at this stage the piece begins to come alive.
I took a few screen caps of some of my reference folders. The top one contains the three main photos I based my Street Fighter piece on. I was in a crunch for time, so I went online and found some great martial arts reference. As you can see, I deviated quite a bit from these photos, but they informed many of my marks. The 2nd image is my reference folder for the "kitchen" painting that I am working on. That's probably the most researched piece I've ever did. And the last image is what's on my computer now. I'm working on a new painting, and am trying to figure out one of the primary figure's pose. Most of the time, I can never get the pose just right in one shot, so I shoot details of the face, feet, hands, etc.. These are helpful because they give me a ton of options to add to the "base" pose. Usually the reference that I print out and work from, is a chopped up from many different photos, and is optimized for my purposes. And like Rockwell said, the photos should just inform your work. I really try not to merely copy the reference, but use it to enhance the world that I am creating in my illustration.
Hope this is interesting to some!?