I used to be the proud owner of an American Express card until I realised that many merchants don't accept AmEx and the account is, for me, far more expensive than ones available from other banks. I once asked a local restaurateur why they don't accept American Express cards and his response was simple - American Express charge merchants 5% commission vs the normal 2% or 3% charged by VISA or MasterCard providers.

Basically, what you've learned in this post about Cape Town (and South Africa in general) is that many merchants will accept your American Express card, but you're far safer bringing along your VISA or MasterCard (just in case you can't use that beloved AmEx one).