This may belong better down in the Pentax forum. I've got that lens and I like it quite a bit. I've only just started with my new camera, so I'm not the end all be all of what can be done with it, but I haven't noticed an unbearable amount of softness with it. I was looking for some good examples I've taken recently, but it's hard to tell which flaws are caused by the lens and which are caused by my hand holding technique!
For example, this one WOULD be a perfect shot to show the capabilities, but it's got pretty bad motion blur that's really noticeable in the larger pictures on the rocks:
There was a good bit of distance between me the guy fishing, at least a couple hundred meters (although I'm not sure the exif default of 2k is right).
Camera: Pentax K110D
Exposure: 0.001 sec (1/1600)
Aperture: f/5.6
Focal Length: 200 mm
Focal Length: 2000mm
ISO Speed: 200
Exposure Bias: 0/10 EV
Flash: Flash did not fire
Also you'll notice that I didn't get the autofocus quite right, and the water behind him is actually in focus while he's not. Since then, I've learned how to use the camera's selective focus points!