According to a 2001 census, 80% of South Africans view themselves as Christian. Of course, what is considered to make one a Christian differs from person to person.
Some South Africans would say that if you go to church every week you're a Christian, while others will attend church only on Christmas Day, and perhaps over Easter. Yet others would claim that going to church means nothing and that it's your belief that makes you a Christian. A large proportion of black South Africans declare themselves Christian even though their Christian beliefs are often a mixture of Western-style Christianity and traditional African culture, beliefs, and ancestral practices.
It seems to me as though this large Christian contingent is quite a mixed bag of variations on Christianity. If you were to dig your hand in to pull out a Christian, each time you did so you may end up with a Christian who believes something vastly different to the previous Christian you pulled out. :D