Okay, I guess I'm the only one crazy enough to try this, but I helped a friend sell some camera equipment. After playing around with the old Nikon F (Non-AI) lenses and one of the Nikon F2 bodies, I couldn't resist. So I bought:
Nikon F2
20/3.5, 24/2.8, 28/3.5, 50/1.4, 55/3.5 Micro, 105/2.5, 105/4 Micro lenses.

After three days of trying, and lots of patience, I finally discovered that the F mount fits fully within the K mount...now I've been using all those old lenses on my Pentax body! The 20/3.5 is an AI lens, and it doesn't fit as nicely as the others, but the rest fit with a little turn - and the 24/2.8 and 55/3.5 even lock in!

They're nice little lenses, they're all quite sharp and have decent bokeh. I haven't had time to do any testing with them, but in 'real world' they've done quite well. Here is a picture of the gear, and I'll follow this with some pictures.
http://www.pbase.com/carpents/image/65238506/original.jpg