Well, my usual routine is a full body, body weight workout circuit, so I can't really say that I put any particular focus on one part of my body.
However, I do put some extra reps and effort into both my abdominal and back muscles. I don't really care for having toned quadriceps, triceps, or biceps, but I do like having a strong core. Having strong abdominal and back muscles goes a long way, especially if you do a lot of physical work such as lifting and moving heavy materials.
Developing those muscles has helped reduce a lot of my back pain from manual labor.