Mashonzha Lounge:
Lounge open: 0700-2200
This is located just outside the BA lounge. It's the new Diners Club lounge and you can longer use DC card to access the Shongolola Lounge. They also accept cash R200 something for 4h. It's small but very modern and an impressive food selection. Some food you will have to warm up in a microwave oven, but also a good selection of cold food.
If you're a smoker this is the lounge you want. The smoking section is even nicer than the small non-smoking:
Yes, that's my microwaved beef lasagne with a Greek salad. The lasagne was very good indeed ^
BIDAir Premier Lounge
Lounge open: 24h
This lounge is located near the passport control on the upper level. This lounge used to be a dump, old and dirty. To my surprise it has been newly renovated and is top notch. A good selection of hot/cold food and drinks. The lounge is one of the largest in the terminal.
Yes, you saw right. Even some bubbly (although not proper Champagne) in the cooler.
If you plan to have some hours at JNB Intl, get a Diners Club card.
I slept good on the JNB-LHR sector in 20A, a very private seat on the main deck. My last leg LHR-ARN was the only spent in economy but it's a morning flight and only 2h.
All in all, a vey good trip with some pleasant surprises ^