Same as OP, I'm still busy with Demon's Souls. I'm taking a few days off now to calm my poor nerves. Haven't rage quit though.
Games I have rage quit are Ninja Gaiden Sigma (I just can't do it!), Heavenly Sword (on the final boss, no less), Homeworld 2 (on the second playthrough. Adaptive difficulty is BS), Fallout New Vegas (became so buggy it was unplayable. Have picked it up again though), S.T.A.L.K.E.R. (it ate my savegames!) and Armored Core: for Answer (2 against 5 on Arteria Carpals? That's just not fair! (Managed to cheat my way though eventually)).
Games I have rage quit are Ninja Gaiden Sigma (I just can't do it!), Heavenly Sword (on the final boss, no less), Homeworld 2 (on the second playthrough. Adaptive difficulty is BS), Fallout New Vegas (became so buggy it was unplayable. Have picked it up again though), S.T.A.L.K.E.R. (it ate my savegames!) and Armored Core: for Answer (2 against 5 on Arteria Carpals? That's just not fair! (Managed to cheat my way though eventually)).