I haven't been there yet, but many of my colleagues...in fact, one is from South Africa. He's told me some.....interesting (meaning scary).....stories also. Particularly in Johannesburg, the crime can be a significant problem. Capetown is better. I'd say wait until you develop a network of local friends who can help you to understand where it is safe and where it isn't. Like any other city, just don't look like someone worth robbing and you'll be halfway there.