K85/1.8
This is a typical portrait lens which I love very much. I've made some great shot from my kids. And when you put this lens on the camera, it's like someone has put the light on. It's quiet heavy (330gr) and a bit bigger then the FA50/1.4 and very usable on the digital camera's, thanks to the green button for stop-down metering and I used it a lot on the Ist*D also because you don't have to look at taking another picture. The depth of field is very narrow wide open, so focusing need to very precise. Thanks to the good focus-screens on the Ist*D and Kx0 camera's with a pentaprisma it's not a bit issue. I think it's more difficult on a Kx00 body, like it was on my Z70.
On a digital body it becomes a 125mm which I personally find even better then 85mm for portraits. I find the bokeh nicer then on the 50/1.4 and prefer this lens to the 50/1.4. The only thing I mis is AF from time to time especially with kids.

Permformance.
The lensperformace has the typical curve with the max performance at around f8. As you can see the performance is comparable to the 50/1.4 with better corner performance and this lens is also about one stop slower. I find it usable wide open, but most of the time the dof is to narrow to be used for head/shoulder shot's. Most of the shot I make are at f2.8 and the graph below show's a bit why. There is very little difference between f2.8 and f4. Above f4 it's better then the Ist*D can record, probably also on the K10D. On the K20D en K7 maybe the lens will become the bottleneck, but I think there aren't a lot of full-frame lenses capable to deliver enough resolution for these sensors.
On a FF body there is a bit vignettering wide open but at f2.8 It's almost completely gone. On a APS body it's even wide open not a bit issue.
There is a bit of CA (I'll given it a 8 in my test notes) and contrast is high (gave it a 9).

Overall a good lens, although I'm dreaming of the other great pentax lenses like the A*85/1.4, FA85/1.4 and the terrific FA77/1.8.
This site seems to confirm my results and here the K85 seems to be even better then the FA77: Yoshihiko website  .