I haven't been to southern Africa, but my Mum has - specifically to South Africa. They travelled all along the southern coast. Mum went on an organised tour, and really enjoyed it. She said it was really good.
Oh, and one of my friends lived there for five years. He said it was really beautiful, but had a high crime rate - he was mugged there.
I think that South Africa will be quite safe for a holiday if you go as part of an organised tour.