I don't breed
purely for temperament, however I would put it up there with any other consideration as regards any other area to be concentrated on. I could have the most wonderful looking ham in the world and if it was slightly vicious I wouldn't even consider breeding from it.
All our hams have lovely temperaments - I don't have any that are not tame, happy and confident and so its not something I have to worry about. But some have taken longer to train than others, and I find handling at a very early stage is a great help in allowing the hams to really enjoy human contact.