Maybe I should point out that both the writer of the article and I are live in Iowa and he was talking about country roads. The vast majority of country roads in Iowa are as straight as a ruler, and he suggested this maneuver when you first notice a car back there. I use my mirror and lot, so most of the time on a straight road, I notice a car when it's 1/2 - 3/4 of a mile behind me. But let's use an example where it's 1/2 mile back there. If the car is going 60 mph it's going to take him 30 seconds to go from point A (where I first notice him) to point B (where I am now). If I'm going 15 mph on the bike, I'm going to travel another 660 feet in that same 30 seconds (another 1/8 mile). So, I've got plenty of time to move to the left for a few seconds, then move back to the right. The point is to clue the driver onto the fact that I'm not a traffic sign or something like that up ahead. This isn't something that I'd do after the driver has begun to move to pass me. Then, clearly he knows I'm there, and shifting around would only be an annoyance at that point.

I tried this out on yesterday's ride and I liked the results.