I think the hate to love angle is so much fun to read because there is this epic amount of passion built up. However they come to understand and change their feelings towards eachother,those feelings will burn with the same amount of passion and be channeled in a *cough* more pleasurable way.
There aren't many things a hero or heroin could do to be completely unreadable. But raping the h/h is definately one.I don't think could forgive a h/h for an extreme violence against the helpless.There are many forms of abuse and violence--but I think sex crimes and severe physical abuse are hard to somach and forgive.