Small regionals and any place the cargo is more valuable than you are..
...sat up front many times from Vancouver-Victoria on any of the little 6-10 seat Otters, and have sat up front from Edmonton-Yellowknife (3/4 of the plane was cargo, you could see cargo from your seat (not sure what aircraft thats used on this route, something a little smaller than a 767-some AC FT'er will know)...both for the entire flight in the jump seat...have done all of this post 9/11.