The sooner they do it, the better.
I haven't read everyone else's posts yet, but the main thing I liked about Randy Orton as a heel was the fact that he played the role so naturally. I remember his monotone voice and how he talked really slow. It always made me want to boo him, and it gave the Faces the perfect ammunition to strike back against him.
Randy Orton is the worst face ever. They should never have turned him face to begin with because it was destined to fail. Every single time they try to make him look like the good guy it has been a complete failure. He is boring when trying to be the nice guy. Let him punt the bosses head and RKO the dads of other superstars.
I never got bored of Heel Orton, Never once. Orton is my second favorite wrestler, next to Punk.
Orton as a heel or a face, I don't care. He will always be one of my favourites. I don't suddenly like someone because or dislike because they turned face. Same when they turn heel. I like the wrestler because of them, not because of alignment or gimmic. However, I can get bored of my favourites still because they can sometimes get too predictable.