I myself am currently replaying The Witcher 2. On Dark mode. I'm about 3 quarters of the way through, and, while I haven't had too much trouble, I would never drop the difficulty. Dropping the difficulty would defeat the purpose of why I'm playing on the hardest difficulty: so that I can have the experience of playing on the hardest difficulty.
When I first play a game, I play on whatever the standard difficulty is, so i can appreciate the experience (except with series I have a lot of experience playing, in which case I'll bump the difficulty up). Then, I replay on higher difficulties, and even if it kicks my arse, I don't drop the difficulty. There have been cases where I just give up and stop playing the game. I got through Gears of War 3 on Insane, right up to the final boss. Then I discovered that, on Insane, the final boss just cheats until you lose. So I stopped playing.
But while some games aren't worth the trouble, I don't drop the difficulty. I either persevere, or I tell the game to fuck off.