I actually use the 80/1.9 on dslrs with an adapter and love it. Surprisingly sharp wide open, sharpens up VERY nicely starting 1 step down and great bokeh (for me). Would only get better in that regard on a MFDB. Use quite a bit of M645 glass on SLRs as love the sharp but lower contrast and nice tonality of the lenses.
There are two versions. The older C version (all metal body, silver ring) are older coatings. The more rare later N version has revised coatings, more plastic, no silver ring. They are equally sharp, etc but the C has lower contrast, the N slightly higher contrast and a bit more veiling flare resistent. I've owned both and no strong prefer either way.
Have N version now and MIGHT sell it (as well as my M645 200/2.8 APO) as need more AF glass, but be warned, the prices on the 80/1.9, especially the N and particularily the 200 APO have skyrocketed in the last year or so. Don't know if from more MFDB users, use by DSLR players (they are talked up quite a bit on various forums) or HDSLR video users, but if you find good copies of either at a price you take tolerate, don't hesitate.
Frank Doorhof would also be a good one to PM on the subject of the 80/1.9 on a back.
http://www.doorhof.nl/forum/index.php?topic=1390.0
