A couple of years ago but we were seeing tens per day in the South. The only problem with Jos's idea of heading North is that there are far fewer large mammals.
I think we spent two weeks in the park, moving all the way down from Pafuri and we were in to the second week before we started seeing anything other than the odd Elephant or Giraffe, far more animals in the lower half of the park.
Yes and no, parts of north can be hard going from a mammal side, other areas can be excellent. Some central parts also very good, but with a fraction of the tourist numbers of the busiest parts of the south.