1. Very. In fact it's the biggest single aspect of the X-T1 that appealed to me when it was announced, and continues to be the most useful aspect of it for me in use. It extends slightly beyond the framing of your question, though... it isn't just that I can see how it's set before I turn it on, it is also the fact that I prefer a marked dial when making those adjustments over a digital menu, regardless of whether the camera is on or off.
2. ISO, Aperture, Shutter speed, and EV comp. I use them all fairly often. Reading everyone else's responses, I think perhaps the reason I use shutter speed a lot (and they don't) might be that I shoot a lot of pictures while also riding bike. In those cases, I usually reach into the camera bag, my fingers find the shutter dial, I press the lock in and click it over in the correct direction 3-4 clicks to get something like 1/500 or 1/1000, all before I take the camera out of the bag, much less turn it on. I can't really take my eyes off the road for more than a split second. This also makes me prefer the fuji lenses with marked ap rings, so I can habitually twist them to the full A stop with my middle finger without looking. On that 5 week long trip, I was able to adjust all 4 of those things while biking, using only my right hand, so I could steer and brake with the left hand.
edit: I also wish the Presets were a dial sometimes, because I switch those somewhat often. I have them assigned to the little button on the camera's face, under my middle finger when holding the grip. Then I roll the thumb wheel to what I want and half-press the shutter, so it's still a 1-handed operation, but when I turn the camera on, I have to look down to see what jpg profile I'm in. Minor annoyance, due mostly to how the other "important" aspects for me are tactile.