I have been eating mostly whole unprocessed foods for a long time before I went Primal, but always liked popcorn, ate it at least 3-4 times a week. In the last few months I decided to ditch the popcorn for a while and see how it goes, and at first I really missed it. Now if I try to eat it, I end up with indigestion for the whole night, so now no more popcorn. Proves to me that you just don't realize how much grains are affecting you until you get off of them for a while.
Also the popcorn seemed to keep me mindlessly snacking, since breaking myself of the habit, I can sit and watch TV or a movie without continually munching on something.