There are as many recipes for Boerewors as you can shake a stick at - and in South Africa there is really only one kind of sausage - Boerewors. Anything else is a curiosity and needs to be bought from a specialist butcher - though some of the more posh supermarkets have started selling 'British Bangers'.
The basic taste comes from the ground corriander seed. Anything else is optional, though most recipes contain vinegar.
In South Africa, every butcher has his own secret recipe. Myself, I use a combination of ground corriander, allspice, pepper, and salt. I also put malt vinegar, though last time I ran out, so used wine vinegar instead which really gave it a nice new dimension. Others add a bit of ground clove and nutmeg, but I don't like it so much. Boerewors should also be fairly coarsly minced.
Other variations on top of that include Cheese Boerewors, and tomato Boerewors which is basically the recipe above with either cheese or tomato added to it.
Every year there is a Boerewors making championship in South Africa - it's quite a laugh.
I'm going to order some of Franco's Sardinian mix soon - if he throws in a sample of the Boerewors mix, i'll let you know what I think