Tried Serendipity (near Naboomspruit, 185km from Randburg) over the long weekend (probably wasn't the best time to try it...).
Stayed at the Boskamp. Really nice area with three large campsites. Lots of shade. Two toilets and donkey-powered showers. Power and running water at the sites (power is apparently not reliable though).
There was another group of campers on the one of the other sites and we hardly noticed each other. Right behind campsite 2, just on the other side of a hedge is a chalet, different story here though... Although you can't really see it you can definately hear it if it's occupied by the brandewyn-het-nie-brieke-nie, check-out-my-new-sound-system brigade Had quite a few bikes / quads going past the camp in the mornings and afternoons as well (although they're supposedly not allowed in this area).
Will try it again over a normal weekend as well as some of the other campsites (Bundu and/or Echo camps).
Fortuner D4-D 4x4
Cruiser 78 4.2D - sold
Prado 150 3.0 VX - sold
Pajero CK DiD - sold