Great idea! Thanks to this thread I also decided to use one of my cameras for monochrome - Samsung NX5 which has more or less the same sensor like K20D. This model is mirrorless with EVF so I set to full monochrome which helps me, as I didn't used BW film for years.
The sensor is little noisy, but that looks quite natural - I also think it is "film like".
When used with ISO set to auto it resembles the way I used one of my film cameras - Pentax MV. Well it looks not so good of course, but the size and weight are more or less the same.
I attached the original pancake lens - SMC Pentax M - 40/2.8 which works great with small camera (thanks to the adapter). I rather plan to leave this lens permanently on.
I do not want to just JPG's as my Samsung produces usually ugly ones. I develop RAWs in Raw Therapee using one of the presets for BW film (this is a great tool called HALT CLUT- several dozen presets for BW films and even more for color ones are available). Just one of the first snaps from this setup below.