I am strictly a commuter. I ride to get to work in the morning (usually before the busiest rush period), and I ride to get home (when it is a bit busier).
I live in a small city in which shoulders are very rare due to the topography of the area. Lanes are often narrow for the same reason. I generally ride in the rightmost travel lane, either in the right tire track or just to the right of it. When going downhill I get close to the 35 mph speed limits, and take the whole lane in those situations. When downtown near my work I take the lane in the 20 mph streets.
There are two roads with bike lanes that I ride on. One is a glorified shoulder, covered with debris. I ride in the bike lane, very near the car travel lane. The other is a terribly designed new bike lane, on a 2-lane, 20 mph street with head-in parking on the right side. I do not ride in this bike lane for fear of cars backing out.
I ride through stop signs and lights only if I am certain there is no traffic in them. I have split lanes to get closer to a light when all traffic is stopped. I always try to wave or say hi to fellow cyclists. I see 8-10 a week on average; less in the winter, more in the spring and fall.