There are certainly a couple of Nigerian companies which have been known not to pay people and who have not honored any terms of the contracts once people have arrived in Nigeria. I'd certainly think twice before working in Africa for any comppany which didn't have a partnership with a European or North American partner - though reading some of the other threads on here, even that's not always a guarantee of good treatment. I do believe that with a partnership at least you'd get paid, because you always have recourse to American or European courts, whilst with a Nigerian company you still effectively have nothing.
I haven't personally had any bad experiences. We can't always get what we want, but I've alwsys been treated fairly, even if sometimes I've had to fight for it. I've had friends who've had some very bad experiences in Africa. After reading some of the posts on the What's New In Africa thread, it would be innteresting to hear if some of the Africans think they get treated fairly by European or American partnerships.