I have driven Tunisia 3 times in my own car, and once in a hire car, no problems.
At night the small towns have no street lights and the children, donkeys, donkey carts and people in general are not well lit, also the mopeds drive on either side of the road without lights. I had extremely good lights on my LR about 400w in all so I found it ok, my mate, with standard lights hated night driving.
I would say it is not as dangerous as they make out but you must drive with caution. I drove a hire car from Djerba, to Douz, Kebili and Bechni, via Beni Kedech and Matmata, again no problems.
Have a look at
http://www.4x4-travel.co.uk "Trip Reports" "2006/7"
Kevin