Brian Kraft continuously updates his post about the X100s with images and PROS and CONS here.

Here some PROS:

• AF improvement… Is it what you’d expect from the latest and greatest DSLRs? Do you really expect it to be? In some respects it is as good, but probably not quite in all– as it’s very different. At least if I’m comparing to my Canon 5D Mark III cameras, which are quite sophisticated in tracking motion, etc. That’s what I have to compare to and probably an unfair comparison.[…]
• Being able to preview your photo in the viewfinder for .5 seconds is like a fresh of breath air to me. On the X100, the shortest preview time was 1.5 seconds or not at all.[…]
• A much shorter minimum focusing distance (with AF) in non-macro mode! Fuji says it’s been reduced to 21 centimeters or 8.25 inches at that seems to be what I’m getting.
• The manual focusing ring is way more responsive.[…]
• Switching between AF and MF, with the re-ordering of the switch on the X100s is wonderful.
• You can now switch between photo previews in a zoomed-in state. If you want to closely examine photos for detail on the LCD or EVF, you can now scroll through various photos with that same view, whereas with the X100, you had to zoom all the way back out, proceed to the next photo, then zoom back in on that one–making it almost impossible to properly compare any photos in that way.[…]

The CONS:

• This does not apply to RAW shooters, but for those that enjoy shooting jpegs, this may apply. Now, I say may, because this is very much an opinion and personal preference. I’ve noticed that when I had the X100s set to standard (0) noise reduction and I shot jpegs at 3200 and even more so at 6400, and even higher, that I was not wild about the way the camera was cleaning the image up. Less noise can be a nice thing oftentimes, but it’s  the trade off that I’m not quite loving–when set at 0. To my eye, it’s almost a smearing of detail–an almost plastic-y look–the way someone may heavy-handedly over-use the noise reduction in a program like Lightroom. It’s not something I initially noticed zoomed in at all. In fact, I think it’s even more apparent when viewing without zooming in. Now, the nice thing is the X100S allows you to set among 5 different levels of noise reduction +2, +1, 0, -1, and -2. I just did a test at ISO 3200 and 6400 settings and shot the same thing, using all 5 levels across the 10 photos and happily I can already tell that I will be able to find the happy balance that works for me. I need to spend more time with it, but I think I’ll keep mine set on at least a -1 NR. I don’t mind a little noise and, in fact, quite enjoy the quality of noise that the X100S has– at least at ISO 3200 and 6400. I’ll need to do further testing to see what my impressions are at the even higher ISOs and what effect the different NR settings do for me.[…]

• […]On the X100, that button was called the RAW button and after a few firmware updates, it became customizable and was the perfect way for me to toggle the ND filter on and off. Now, with the X100S, you have to dive into the menus to toggle the ND filter on and off. I’m not happy about that and I do hope a firmware update can address that and add the ND filter to the Q button options. I do realize that the function button can be assigned to the ND filter, but I like that assigned to my ISO.[…]

X100s: AmazonUS / BHphoto / Adorama / AmazonDE / AmazonUK (will be shipped on March 11, according to R. Bachmann)
X20: AmazonUS (black – silver) / BHphoto (black – silver) / Adorama (black – silver) / AmazonUK (black – silver) / ebayITA /  / AmazonDE / AmazonITA /

image courtesy: Brian Kraft (PROS and CONS / initial photos / more photos)