I have flown both JFK-JNB (via Cape Verde) and ATL-JNB (non-stop and via Cape Verde). I think that SAA is a very good airline. The food, the service and the entertainment is quite good, if not always excellent. I found the staff, in particular, to be friendly and willing to chat when not busy.
The last time I flew with them was in August 2001. The food was abundant and very good. They also offered "unlimited" snacks throughout the flight (Haagen Daz ice cream, Snickers ice cream bars, fruit, juices, crackers, cookies, etc.). Drinks also flowed freely but don't have too much alcohol because it has different effects on the body at that altitude and for that duration.
I seem to remember that there were 3 movies and assorted short film and news shows on my flights. The audio selections were varied and good as well.
As for passing the time, I tend to get up and make my way to the back of the aircraft about 2 or 3 times during the flight. You meet the most interesting people hanging out back there. Conversations range from sports to sex to travel stories. Try it, you may like it!
The only problem that I have had with SAA was once when I was goin ATL-JNB-CPT. When the plane landed in JNB the ground staff removed all of the luggage and the CPT passengers had nothing when we arrived at our destination.
Have a great flight and enjoy SAA.