C'mon David...
Amit didn't ask for an ill-informed compare and contrast essay on the US and South Africa, he asked about safety issues he may encounter during his stay.
My wife is South African, her family still lives in Jo'burg and we've been there several times together. My take is that the stories of rampant crime in South Africa are exaggerated, but crime is a problem there. Both my wife's uncles have been held up at gunpoint over the past several years and you'll find that many of the homes in Jo'berg are quite fortified with walls, gates, and private security.
However, it has always seemed to me to be perfectly safe to walk in most areas during daylight hours (at least the areas that you would be prone to go to as a tourist/businessperson). We even went into the downtown area during the day, which some people had said was a dangerous area, and we didn't feel unsafe.
As for the stories about not stopping at red lights, I think they are also somewhat exaggerated. Perhaps some people do this, but in my experience, during daylight hours, the rules of the road are followed just as they would be anywhere else. At night, in desolate areas, my wife's uncles would stop at a red light, check for cross traffic and then proceed through the intersection (treating it as a stop sign, rather than a traffic light). To drive through an intersection without stopping would, of course, expose you to more danger from a serious traffic accident than from a car-jacking.
In general, you'll find the people there to be very friendly and helpful, and the infrastructure to be quite modern. The Sandton area is especially nice. If you use the precautions you would use as a foreign traveler in any big city (yes, even Canadian ones, David) you'll be fine. If you have 5 or 6 months there, be sure to venture out of Johannesburg and explore as much of the country as you can. It is a beautiful place.
-Ryan
PS - David, we're so lucky to have you on this forum to share your "expert" advice. Just so you know, a "California stop" is a term that simply means slowing to a crawl rather than a complete hard stop before proceeding through a stop sign or making a right turn at a red light. Despite whatever "legend" you've heard, people in California don't drive straight through stop signs or red lights (at least not with greater frequency than they do anywhere else in the world) Tell you what, I won't post ridiculous mistruths about your country if you refrain from doing so about mine.