I bought the Fujifilm X-Pro 1 after reading many-a-review on its high-quality images from its APS-C sensor and its 35mm or 60mm lenses. I really bought it because it looked awesome with its metal body and killer retro appearance. Admittedly, it sat around for a bit while I continued to use my DSLR for many projects. I noticed that one photographer who was shooting product and portraits claimed to move exclusively to the X-Pro 1 for all of his professional work. I was pretty intrigued by this, considering the photographer was doing some high-quality studio work.
I did love the image quality from the camera and the 35mm fixed lens. The f/1.4 on the 35 is killer, and I was getting very professional images coming off the camera from everything from outdoor to studio images. I started to use the camera more and more in place of my dSLR (when I could). Basically, I could use it in almost any case, except those that needed high speed focusing. In photographing studio product, food photography, street photography, and portraits, the X-Pro 1 did as good as a job as my other digital cameras.
ON THE STREET
With a light, small body, the X-Pro 1 doesn't appear to be the obvious professional camera, which often requires large, heavy lenses. Fujifilm has put out some really excellent glass, with the 35mm and the 60mm providing sharp images comparable to the highest professional grade lenses of its competitors. The 18 mm f/2.0 seems perfectly adequate to me (although other have rated it slightly less sharp than its brothers). Fujifilm has announced a 14mm and an additional zoom lens to this lineup, hopefully signaling that they will continue to produce the cameras with these mounts.
I think my choice to buy the 35mm initially was a good one, as it gave me a standard lens (about the look of a 50 mm on a full frame camera) with a shallow depth of field (1.4 at its maximum aperture). The 1.4 allowed me to shoot like I was on my 1.2 from other manufacturers and portraits and food photography continued to have an awesome bokeh.
IN THE STUDIO
Under controlled lighting, the X-Pro 1 is as good as any APS-C sensor out there. It seems to handle the low light very low, and I have noticed less need to smooth over dark areas that traditionally had noise in them on previous sensors. When shooting RAW, the camera allows you down to an ISO of 200, but I had not seen much noise up through 800 or so.
The sharpness of the 35mm lens has been phenomenal on a series of food photographs that I was shooting for personal work. Examined at 100% and even 200% in Lightroom has been astounding. In addition, the f/1.4 on these lenses is an additional plus for the whole system: the possibility of such a wide aperture suddenly gives the system an extra professional advantage. The bokeh of the 1.4 is excellent for portrait and product alike. I found the relative weight of the system more than friendly when maneuvering around a product shot quickly.
THE FUTURE OF THE X-PRO 1
Fujifilm released the X-E1 after the X-Pro 1 and many found the specs to be similar. In fact, Fujifilm left the same sensor (16.3 MP) in the X-E1, complete without the anti-aliasing filter, giving these sensors excellent sharpness. They eliminated the rangefinder from the X-E1, which was to the dismay of some, but to others it was unnecessary, and the drop in price that accompanied the X-E1 was very interesting for those wishing to have a professional grade system in yet a less expensive option. The focus system was also improved in X-E1, giving 
the it also some advantage over the X-Pro 1. In the future, what could make these cameras any cooler? Not much, except maybe a full size sensor in the X-PRO 1 giving it a true rivalry to the Leica models. Surely, the next X-Pro 1 upgrade (assuming there is one) will improve its focusing and be even better, but with the recent drop in price from $1700 to $1400, the X-Pro 1 is a really great option for those who want a killer camera for travel, studio, or street photography.
DISADVANTAGES OF THE X-PRO 1
Focusing speed
Changing focus points
Occasional metering difficulties
ADVANTAGES OF THE X-PRO 1
Excellent sensor quality
Excellent lenses, especially 35mm and 60mm
Lightweight, yet strong metal construction
Optical and/or electronic viewfinder and rangefinder
Low profile and a lot of fun