I just got one of these a few weeks ago and am very happy with it. I don't have many pics to show yet, just stuff around the backyard, but I did take it to a concert on Saturday and had to shoot wide open(2.8) and at ISO 3200. I was pleased to find I still got some very useable shots with my K20.
The f/2.8 shallow DOF makes the subject pop here.
hopefully I can take the lens outside for some daylight testing this weekend.
In my initial outdoor tests, I find the bokeh to be surprisingly good, so I may use this lens for some portraits even. Also, though the screw drive AF is pretty noisy, it is not really slow compared to other screw drives. I have rented a couple of SDM lenses before and they are really fast and quiet, but they also cost MUCH more $$. FWIW, I can deal with this lens for now.
Highly recommended!