Knowing me well, he claims that I'll feel imprisoned by a one lense camera eventually. I am painfully aware of that psychological fact, although I'm also fascinated by the simplicity and restraint of having onely one lense to maneoeuvre.
With the X100, you have a 35mm equivalent lens, with no options. However, if I could have only one camera with only one focal length, it would be this one. Over the past year, I have shot far more with the X100 than with the D700.
Part of the reason is that it is always with me. Another part of the reason is that I mostly photograph people and the stealth factor of the X100 is such that people ignore it and I get the most natural, unposed slices of life possible. It is silent.
On the other hand, while there is a click from the X-Pro1 shutter, most people in a room will not hear it. The X100 has the best fill flash capability I have ever encountered, and with sync up to 1/2000th it is extremely useful outdoors. Shadows open up, as if the level of ambient light was higher, but there is no look of flash. Flash sync on the XP1 is 1/180th and there is no built-in flash.
If acquiering the Pro, my priority would be 1) the 35 mm, 2) the 18, 3) not the 60 mm - I'd probably use it very rarely. I fear I'd go for a 35 eqv., when Fuji is likely to release one next year. Then I'd have (eqv.) 28, 35 and 53 mm - which doesn't sound very wise, does it? The 28 + 53 somehow make the 35 superfluous, without really doing its work.
Of course it depends upon the way you see, but I find a lens in the 90mm equivalent range very handy. In the case of close-ups, it can put a bit of distance between you and the subject. Less chance of blocking the light and less chance of losing the shot if the subject is shy. A lovely focal length for head-hunting at a party or gathering. Shooting wide-open, the background will be softened a bit, putting more emphasis on the subject. Used as a long-normal lens, one gets a bit of compression of perspective, making it easier to relate two subjects.
At this point, only the 35mm (53mm equivalent) has arrived, and find that I am reaching for the X100 frequently. If the 60mm (90mm eq.) is a long normal, the X100's 35mm eq. is a short normal. The 18mm (27mm) is very different in character in spite of the small difference in focal length. It is clearly a wide-angle lens. At 76.5° compared to 63°, perspective opens up and the image takes on a three-dimensionality way beyond the normal focal lengths.
It is at the threshold of environmental portraiture, and I used my 28mm Perspective Control Nikkor a lot for exactly this purpose. The Fujinon lacks the shifting ability of the Nikkor, but still can be used. As long as the subject's head is more or less in the middle third of the picture area, foreshortening is not a problem—just don't place their head in the corner of the image! The shorter the lens, the more subjective the portrait. Aside from the psychological effect of the lens, it is just a handy focal length for many things, nice for landscapes, as an urban walk-around lens, its width captures buildings easily where distance is not available with the 35mm, nice for interior shots as well.
That said, it is not nearly wide enough in many cases, and I most certainly will order the 14mm (21mm) the moment it is announced. I do have the 14-24mm Nikon and with a range of 84° to 114° it does amazing things with perspective.
I don't think that there can be a lens that is "too wide".
I love everything I've read about the Pro, and I don't mind the extra weight - and certainly not the extra size, on the contrary - but their initial lense choice forces me to either vote for the 100 and believe the fixed 35 mm is enough - or the Pro and use the "poles" 28 and 53 mm instead.
Simply, you can not go wrong with either—or both. In the hand, I notice no weight difference, even when picking one up after the other. The controls are the same, though placed a bit differently. It only took a minute or two to reach a comfort level with the XP1's differences. The shooting experience is very similar. Now that I have the XP1, I would never think of getting rid of the X100. Though they operate in a similar fashion, the X100 is the camera I will always carry every time I step out my door with nothing in mind to shoot. So if you go X100, you can add a XP1 later as I have done.
But, not to forget, the Pro has a better sensor, more MPs, and apparently much better handling. No, this isn't easy at all!
While the sensor on the XP1 is state of the art, the X100's sensor has variable spaced photo-sites to allow optimum light-ray entry angle at the edge as well as in the middle. I expect it has a low pass filter, but minimal. Sharpness is astounding. In an optical lab, I would guess the XP1 image quality is probably better than the X100. In the field, both are capable of the highest quality you can possibly imagine. At this point, Adobe is still working on XP1 compatibility with RAW images, but the JPEGs are astoundingly good. (I am shooting RAW+JPEG currently.)
A difference between 12MP and 16MP is hardly significant photographically. Either would produce large prints with great clarity and quality. The X100 is slightly smaller, but very well designed for hand-holding. Both cameras are very comfortable in the field. No "much better"—hardly any difference. It may be unfamiliarity since I have had less than a week with the XP1, but I find myself hitting the occasional button by accident. Not an issue, a tap on the shutter button and it is ready to shoot.
Both are a pleasure to use, and the results are about as good as it gets. When I take to the streets with the XP1, the X100 will be in my pocket or pouch.
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larry!
http://www.larry-bolch.com/ 
