One of the busy thoroughfares in my area has nice, wide flat paved shoulders. Unfortunately, it's the exception, rather than the rule. I use it for my longer rides (30mi+). Mostly, I ride atop the white line, or just to the left of it, trying to miss as many potholes as possible.
"The road to a long biking life is paved with a wide, flat, gently sloping shoulder", me