The only "pocketable" camera is the Pentax Q. All of the other cameras might be "overcoat pocketable."
Personally, I use a Olympus E-P1 and Panasonic 20mm f/1.7. Is has very little depth of field wide open--when I take a picture of my Newfoundland dog, full body, I can't get her nose and eyes sharp at the same time. That is a very small camera where size for carrying and the ability to hold it comfortably for me is the limit.
The fixed lens compacts by Fuji, Nikon, Canon, and Olympus would be a smaller. But not by as much as you would think. The Pen Mini and Nikon J1 are sort of in between depending on the lens. The interchangeable lens mirrorless can be small, depending on what lens you put on them.
The Pen is nice and I enjoy using it, but to be honest, I seldom get anything good out of it--nothing better than snap shots. The idea of a small, always-carry-camera is nice, but I need to put in effort to make good images and that is not the camera I grab to do it. My Pen has given me records of places and friends, which is why I keep it, but it has not been the tool for great imagery for me--some folks have done great work with this camera, but they are also using this as a primary tool and working hard on their photography.