Within one foot? Twice in ten years of commuting, at a low speed differential.

Within two feet? Maybe a once a year.

Within three feet? Once or twice a month. I don't let these bother me if the speed differential isn't high (the usual case).

This is commuting 2-3 times a week, mixture of 2-lane and wider 35 mph roads, and some 4-lane 40-45 mph roads. I ride near the center of the lane on the narrow-lane 4-lane roads, and ride the right side of the lane on the 2 and 3 lane roads that are mostly wide lane, low traffic, or both.