Not really a fan, because most iterations just end up being annoyances or just make the game more tedious. Also I'm not a fan of hardcore modes that destroy all your progress just because there are so many factors that could lead to a death that isn't their fault. For example I've had people come to my door or something, and many games like MMOs you can't really pause, so do you either completely ignore someone at your door, risk somehow getting killed to run to the door, or do you get to a safe zone, spend the time logging out and then pray the person is still at the door?
Also most games really don't seem to be designed anywhere near the intention of being played on such a mode. For example Left 4 Dead, realism mode is absolutely dreadful. I've breezed through expert mode and both games without any real difficulty and have had a ton of fun (except for dead carnival, which made me pull at hair at crescendo events) yet realism expert is a terrible experience. And it is in my opinion the reason why this is, is because the game was designed around the fact that the players are able to normally trek through a level taking multiple hits, and finding various items. But in realism mode, that enormous stretch is damn near impossible to get through because you essentially have to play the game so perfectly that it is almost inhuman and the slightest chance of random bad luck screws you completely to no fault of your own.