I flew for Desert Wind Air Service, which is very similar to Northern States. Both companies operate for Pictometry, and do the same kind of flying.
It is definitely a young mans job... on the road for 8 months out of the year, and bunking up with another pilot. It was a lot of fun, and a great learning experience. At DWAS we didn't have to get "released" by the boss before flying, and he didn't mind us ferrying at night or IFR. I built up 1000 hours in my two seasons there, and then went to ExpressJet.
The most fun for me was that when they wanted us to reposition, they would say "we need you in Charleston by Friday", and it would be a Monday in San Francisco. But they didnt care how I got there as long as it wasn't vastly out of the way, so I would visit friends in Arizona, then friends in Dallas, then make it to Charleston.
Over-all it was a good experience and I would recommend it to any low time pilot.