I've been using one on my K-01 since April, and I'm very happy with it. I've used it wih Olympus, Nikon, and Yashica/Contax lenses.
It is necessary to put a piece of tape over the aperture control button on Olympus lenses so they'll stop down with the aperture ring. Y/C lenses need about 3mm clipped off the end of the aperture lever so it doesn't protrude too far into the Pentax chamber; that amount doesn't affect the capabilities of the lens with Y/C bodies.
I have only one Nikon lens, a non-AIS Nikkor-Q 105mm f/2.5, and I had to shim the mount by 0.8mm so it would even the mount with the lip of the aperture ring. 1mm would have been better, to get the flange focal distance closer to the original Nikon register, but I didn't have small washers that thick. Now it attaches smoothly to the Pentax, however, and infinity focus is acceptably sharp at f/4 and above.
The only problem, if you want to call it that, I've encountered is that if non-Pentax lenses are left on the mount for long periods of time, they compress the tension springs on the underside of the mount, making Pentax lenses fit slightly looser than normal. The Adaptist site gives a warning about that and tells how to retension the springs. I haven't retensioned mine, and all my Pentax lenses still work just fine with the camera. The contacts all make contact and the autofocus screw works just as it should.
Here's the K-01 with an Olympus OM Zuiko Auto-S 50mm f/1.8. The lens is marked Made in Japan, which is arguably the sharpest of all the OM 50/1.8 series.
And a shot made with this combo: