I'm considering travelling to Jo'burg, most likely by myself. I hear various stories as to how safe it may or may not be, so am keen to hear other's views.
Personally, I'd take a lot more care around Johannesburg (particularly downtown) than you would at home but by all accounts they have been putting a lot of money into lowering crime in Johannesburg (even enlisting the aid of Rudolph Giuliani) before the 2010 World Cup. If you are going to Johannesburg, make sure to get out of the city and visit places like the Pilanesburg Game Reserve. Also, I'd recommend taking a tour to one of the townships (like Soweto) - but I wouldn't try to do that on your own, its better to rely on people that know and understand the area. almost 11 years ago
I would tend to agree with wilskim. Take care around Johannesburg if you are in a taxi make sure you lock your door. Always be careful of your backpack and other items and always be on the look out.
I wouldn't travel Johannesburg on my own at all, if i was you i would find a group and do day trips etc. I went on my own where i was there and for a females in her mid twenties i felt very venerable to people even at the airport let along in the city.
Take care and be on the look out. People are always willing to help you out as well over there so choose the people you ask questions off carefully! almost 11 years ago