I had read in TA before we left for Africa that baggage theft was a problem at the Joberg airport. Two weeks ago we flew from Cape Town to Lusaka and changed planes in Joberg. When we arrived in Lusaka the lock had been cut off my bag and it had been gone through thoroughly. Nothing was stolen. All our valuables were in our backpacks which we carried on. I told the SA rep in Lusaka and she shrugged and said that they were looking for laptops etc .(to steal), they knew theft was a problem and they were working on it.
Be careful. I know theft is a problem everywhere, but this is my first in 30 years of flying. I'd even go so far as to split up any nice shoes/boots with your traveling companion.