This is a good reference, with pictures, on the pin problem and what to do about it:
Sears 60-300(auto aperture, push pull zoom): Pentax SLR Talk Forum: Digital Photography Review
Note that not all lenses with that dreaded Ricoh "pin" are problematic. I have had like four different Ricoh K-mount lenses over time, and none of them ever got stuck on my K20D.
I think what it boils down to is this: on some lenses, the pin is pretty much cylindrical and sticks out, with sharp(ish) edges, and that can get caught. The pin looks like that on the thread cited above.
But on the lenses I had, the "pin" is more of a gentle ball-shaped protrusion, which glides in and out of any obstacles (like the Pentax screw-drive opening) without getting stuck.
Your mileage may vary. I don't know if there's any definitive reference showing which lenses are which type -- but usually, it's pretty easy to remove the pin if you wish without causing any permanent damage.