Hey Pundit,
Have MTB'd in the area and it was great. You can do most of the Clarens cycle race route if you head out up the hill towards Bethlehem and then hang a right at the top and muck about on the district roads there. Also on the way to Golden Gate is a road to the right for a bunch of game farms and the Clarens Castle. That road heads straight for the Maluti's, with some excellant climbing and brilliant views.
There are also a bunch of 4X4 trails that are apparently available for riding. Perhaps some of the other hubbers have some ideas about these?