I've had my X100s since release as a compliment to my 5DIII. I'll list my current setup and usage.
5DIII, Canon 50L, Canon 85L II, Tamron 24-70 VC, & Canon 70-200 IS II
and... Fuji X100s.
What gets more use? The Fuji X100s by far.
Daily Shooter: Fuji X100s - It is small enough that I keep it in a small case and toss it in my bag every day.
Street shooting: Fuji X100s - Small, discreet, silent
Portrait Shoots: 5DIII, 50L, & 85L II with Fuji X100s as a compliment
Event Work/Photojournalism: Tamron 24-70 & Canon 70-200. Although, I did shoot an event last night with the 5dIII + Fuji X100s for an 85mm + 35mm prime combo and it worked out pretty well! For paid gigs though, I'll stick with my zooms.
Low Light Work (low action): 5DIII and Fuji X100s (the Fuji actually handles noise "slightly" better than the 5DIII).
Low Light Work (action): 5DIII - Fuji AF is too slow in low light for action shots for my tastes.
To answer someone's question earlier about one-handed shooting with Fuji X100s - Yes for shooting, not for changing many settings. With one hand I can grab the camera, turn it on, swap between OVF and EVF, and take a shot. (worst case scenario, with a neck strap and X100s pressed against your body, you can change shutter speed, aperture, etc).
AF - I have found the Fuji X100s AF "good enough" for me probably 90% of the time in good lighting (phase detect AF only engages in good light. in low light, it uses the slower contrast AF which is the same as the original X100)
Usage percentage - I'd say I use my X100s 75% of the time, if not more. I end up bringing it for most professional work too, so it gets used a lot. It is also the most fun camera I have ever used, so that helps.
Limitations & Quirks -
*The X100s is still not a "perfect" camera, and does still face some limitations. The AF is nowhere near 5DIII/OM-D levels. In low light, it gets worse as mentioned above.
*Fixed 35mm lens - Great as a second camera, but I would never own it as my only camera.
*Still room for improvement - The focus peaking in MF could be better; Exposure compensation dial doesn't work in Manual mode; no customizable Q menu, etc. Basically, there are a few small things that could be better but Fuji is in my opinion, the BEST at offering users frequent software updates and listening to user feedback.
*Image Quality - Pretty amazing for APS-C. It is the best IQ I have seen come out of any APS-C sensor camera and is mostly indistinguishable from the comparison shots I have seen with a 5DIII + Canon 35L and the Fuji X100s. My 5DIII + 85L II on the other hand, well... nothing short of a $10,000 kit can top that combo.
JPG vs. RAW - Both are great. The Fuji has one of the best JPG engines of any camera in my opinion. However, I still mainly shoot in RAW. You may read things about issues with the X-Trans sensor and Adobe, but rest assured that these issues have been resolved to the satisfaction of 95% of Fuji users (there will always be the remaining 5% pixel peepers).
Overall I've never owned a Fuji before the original X100, but I am smitten. I'm biased because I love it so much. I can't wait for the X-pro 2 to come out (which will hopefully be an interchangeable lens X100s).