i use the range finder mode 99% of the time. not only can you see people walking in to the frame as you snap a picture but for low light photography at slower speeds it is fabulous.
we were in montreal in some of the most fabulous churches and had to shoot high iso and still slow speed.
with the range finder we found it so easy to focus and lock visually on a subject , let the 2 second timer trigger the camera and get shake free shots.
i wish we could do that with the dslr but the view finder goes black once the timer starts and you have no target to lock on to.
the x100s did a great job . these are all 1600 iso ,handheld at 1/20 or less