I read 120 Days, once. Not a pleasant read; I found it bearable only because the sheer implausibility or impossibility of many of the acts put it firmly into my mental "cartoon violence" bracket.
I mean I guess you could *do* many of the things De Sade writes about, you just couldn't survive most of them for very long, or at all. OK, death is the object of many of the torture scenes, but the characters take unreasonably long about it. :/ Even the things that don't involve actual mutilations would still kill you pretty rapidly, even back in his day when hygiene wasn't too good generally.
We had the book because my all-things-cute-and-fluffy, Hello-Kitty-seat-cover-using, kiddies-anime-loving wife inexplicably bought it, and read it, without batting an eye. I still to this day have no idea why.
I wouldn't vote for banning all this sort of stuff, but I think I'm with jvasilatos...