Summary: This lens is said to "one of the best lenses for Pentax". Please be the owner of this lens if you use Pentax. But I'm sad not to select the color (shilver or black). Now I always use this lens with K10D. Focus is severe. So I think it important to "practice" with this lens.
Summary: I use the 31 Ltd on a K10D. It is one of the finest lenses that I have ever used and compares favorably with Zeiss/Contax prime lenses that I have used previously. Images are so crystalline that one would think that there was no glass whatsoever between the subject and the sensor. Two drawbacks are the nearly useless built-in hood and a moderate degree of barrel distortion.
Summary: Best lens ever for street and landscape photography. Ridiculously sharp, and wide open lets you shoot hand held in very tough lighting conditions. Metal body is a pleasure. If you are comfortable walking a bit to frame your shots, rather than using a zoom as a shortcut, the reward is improved image quality. The contrast and bokeh are pro-grade; cannot recommend this lens enough. Note that this 31mm film lens becomes a 50mm normal lens on a 3/4 sized digital sensor.
Summary: I have purchased it for the anthropological field research. It appears to be very good choice. It is impressively sharp even at the corners and good metal body. If it would be dust and moisture resistant, it would be the best lens in world :-).
Summary: This is probably the best Pentax prime lens. It is very sharp at all apertures, incredible bokeh, contrast. I just can't find any flaws. The only thing I could say on the not excellent note, would be the slightly big size.
Summary: The FA31/1.8 has a legendary status amongst Pentax users, and my copy has not failed to impress on my K10d body. It is sharp at all apertures and the colour rendering and bokeh are superb. The construction is all metal and the feel of the focus ring is excellent. The only flaw in its performance is slight chromatic aberration in high-contrast out-of-focus areas, but this doesn't detract from the overall image quality and is more of a quirk than a problem.