Just wrote a bit about this on a different thread but I guess this is a pretty appropriate place to post my experience with the new keyboard so far.
Have been playing around with the rMB in-store on a number of occasions since I first became aware of them by an accidental encounter at an Apple Store in NYC back in April. Hadn't really been thinking about getting a purely personal laptop for a while, being one of those people who had gotten used to the "laptop-as-powehouse" idea over the years. Have had iPads for a while, currently an iPad Air which was doing an OK job at filling the role (of personal go-anywhere machine). But really only an OK job. I like the iPad for many other reasons but a laptop replacement, it really isn't. Even with a bluetooth keyboard, at least not for me. Lucky it's convenient for using around the house like a radio for podcasts, or for games like Real Racing (holding the iPad like it's a steering wheel is something a laptop can't do), or it would have no use to me anymore.
So like many people, I instantly warmed to the charm of these machines - a full OS X machine with a retina screen and no practical difference between it and the iPad Air in terms of portability? Yes please. And then of course the two main question mark issues did come up for me, like for most people. The single USB-C port and the keyboard. Was also a bit hesitant about what seemed to be an extremely low CPU spec for this day and age, but that went away pretty quickly once I started using one. Also, seeing that even the base model got benchmarks that were identical to or better than my top-of-the-range i7 MBP from 2010 - this put things in perspective somewhat.
Anyway to the keyboard: Yes, of course it felt weird at first. Goes without saying. Did it feel potentially deal-breaker weird to me? At first it kinda did. If it weren't for how damned attractive the machine was in every other way - and I mean attractive beyond just aesthetics - I could easily have taken a pass. But it just ticked so many boxes, reminded me of the happy days of the 12" G4 Powerbook and just how fabulous it was to have a real computer in that form factor. It even made me resent my trusty iPad Air, just a little. So the keyboard, above all other factors, became the one thing that I realised I was going to have to investigate and come to a decision on. I quite easily got behind all the other controversies, one USB-C port is something I didn't see coming but now that I've thought it out for my use, it's actually pretty clean. I mourned the loss of magsafe a bit and still kinda do because I always thought it was a pretty remarkable bit of design, really symbolic of the kind of innovative cool stuff Apple does sometimes. But the trade-off you get with USB-C is not bad.
Did I digress again? Maybe it's because I'm really having a great time typing on this keyboard..

(OK let's not exaggerate). But here's how it worked out for me. I must have been about the 10 millionth person to open the first text input app they could find on an in-store demo rMB (the notes app) - because every time I launched notes, it was always already full of other customers' babbling tests to see what it was like to type on. At first it felt noticeably annoying. Somehow the key presses felt really clean and snappy and in theory, precise.. and yet I just kept making mistakes. Then to correct the mistakes, I (like everyone else) discovered the weirdness of the reshaped arrow keys. I left the store that first day a little confused but if I'm being honest with myself, already sold. In fact, the machines weren't available anywhere yet (I asked) otherwise I may well have just bought one on the spot. Went back again another day while still in NYC because the whole thing was nagging at me (and I was hoping that somehow magically stock would have appeared). Spent a considerably longer time using the machine and within less than an hour, all my accuracy mistakes went away. But it still didn't feel right.
Got home to Paris and continued the investigation. Eventually I settled on the spec I wanted and was ready to order, somewhat irritated that the list price in France for the model I wanted was hundreds (I think around 400) bucks more than if I'd been able to get one in the states. Grrr. By this point, I was completely over the accuracy problems with the keyboard and it was also starting to feel somewhat not weird. Dare I say it, nice-ish. But, I (like many people) noticed that my hands felt inordinately tense and my fingers seemed to get tired faster than they should have after reasonable bouts of use. Nevertheless, I placed my order online (if anyone knows how ridiculous the french keyboard layout is, you'll understand why my purchase had to be a CTO since they only stock french keyboard models over here).
Went back to my local store a few more times and decided I'd try to figure out if there was something about the way I was typing that wasn't helping things. After a while I came to the realisation that I was reacting to some instinctive preconceptions that were wrong. It seemed to me that, because the key travel is so significantly sheer compared to what we're used to, my instincts were to tense up my hands and to keep them hovering over the keyboard rather than resting my fingers like I'd usually do. I suppose this was because since it felt so delicate, the natural reaction was to make an effort (in my case a subconscious one) to keep my fingers tensely held above the keyboard because it seemed like if you didn't, you'd be accidentally pressing keys all over the place. So I decided to just relax and even if it felt counterintuitive, just let my hands chill on the keyboard and type with casual effort and no gingerness to keep unused fingers floating in the air. Lo and behold, it worked. Turns out that yes, the keys have ridiculously little travel, but it also turns out that they are snappy little buggers as well. So even with my large and hefty man hands plonked down at rest all over the thing, no keys ever got accidentally pressed. Kept at it for a while and found to my surprise that the fatigue from longer periods of use was now also gone. Since receiving my own machine, I've found that it's all good - having retrained my muscle memory to not type like I'm walking on eggshells, I'm actually starting to like it a lot.
So, in recap: Weirdness at first - check. Thoughts of it being a showstopper - check. Loads of errors and frustration at first - check. Persistence and no quick judgements to give it a chance - check. Typing errors completely gone but experience still feeling weird - check. Weird feeling goes away, starts to feel natural and pleasant but unexpected fatigue kicks in - check. Observation of what I'm doing differently to see if that's contributing to my feeling of fatigue - check. Intentional effort to just chill and type, ignoring the misleading feeling that the keys need to be tip-toed around - check. Surprising discovery that the keyboard, despite being ultra low-travel, doesn't accidentally trigger when you let your big man hands rest on it - check. Happy experience achieved.
That's my take. Of course YMMV very much applies here. But I'd encourage anyone who's still fighting with the keyboard and trying not to hate it to try to be observant about what their hands are actually doing while typing on it. If you find that your hands and fingers are involuntarily being held quite tensely and that you're bashing at the keys to compensate, try seeing what happens if you just let them rest comfortably on the keys with your wrists relaxed on either side of the trackpad. Worked out pretty well for me.