Mbeki set up what's happening now in South Africa in several ways. He subverted the ANC's internal democracy, centralising power in the presidency, he started the tradition of riding populist demagogues to the leadership even if he wasn't one himself, and he pushed Jacob Zuma to the limelight as someone he thought he could ride as a substitute for his own lack of the common touch.
The second edition updates some events like the rise of Jacob Zuma as Mbeki's heir apparent, and the chaos in Zimbabwe though naturally with such fast-moving events, you can't expect the book to be up to date. It does however provide very useful background even for events that overtook it.
I don't agree with everything Gumede says but separate out the opinion and the fact is pretty good on the whole: he seems to have real insider contacts.
Some of his nostrums -- more state intervention in the economy for example -- are not terribly likely to have had a significant effect without a much wider change the style at the top -- but he presents a compelling case that South Africa's first 15 years of democracy, the Mbeki era (even if most see the first 5 years as belonging to Mandela), are a big disappointment. From the mismanagement of the HIV-AIDS pandemic through the glacially slow implosion of Zimbabwe, it's hard to see anything that the ordinary person would count as a success. Managing the economy more prudently than the apartheid regime should count perhaps as a bigger success than Gumede credits Mbeki with. However, he does have a good point that in some sense, the government may have had it backwards. Whereas other emerging economies have at times managed to get away with talking fiscal conservatism, while acting a little socialist behind the scenes, Gumede accuses the Mbeki-ites of doing the opposite: talking left, while acting right. The effect (I am guessing, he doesn't spell it out) is little delivery, while frightening off investors.
Overall, the book is a compelling read, despite the odd editing lapse (some unnecessary repetitions, the odd sentence where it becomes hard to untangle the references). Strongly recommended for anyone wanting to understand current trends in South and Southern Africa.