I purchased the Nikon S2 last August. After having it repaired and serviced, I was officially able to start practicing on the old film camera last fall. We are circling back to having the camera close to one year now and I can look back to see how I have improved and starting shooting more confidently with it.
The hardest part for me with shooting documentary with the S2 was predicting the action and pre-focusing. For so long I only used a SLR and DSLR camera body that I became used to shooting the action when it happened because you can focus quickly with these type cameras.
The rangefinder is a completely different beast. You must pre-focus and predict. I am no fortune teller but I can tell you that planning a shot before it happens has actually helped me. Sometimes a little discomfort is good for the soul. I think my downfall in photography is I became 'too' comfortable.. therefore, my work became stagnant.
I like seeing a new side of my work just by shooting different gear. It has forced me to approach scenes differently and have a plan more so than to just go out and shoot.