I find that all this attention to gaining a few mpg often comes at the expense of one's attention to the road and other vehicles, and by nature of the speed variations, can sometimes even pose a hazard, as you mentioned. Just think what will happen when a million more Prius drivers are "pulse and gliding" to work in the morning. I also think if you are going so slowly as to cause other drivers to flip you off or get upset, it is ultimately a strategy that will backfire by further polarizing the "Greens" vs. the SUV drivers. I hate when I see a Prius holding up traffic like an old VW bus.

Why not just drive the car as you normally would drive a car, perhaps making a few subtle changes? I keep my the freeway speed between 65-70mph, back off slightly on grades, and minimize the A/C use when possible. Sometimes I use electric mode the last few miles home at 38mph on a lightly travelled boulevard. All of this allows me to achieve 45 mpg overall without any stress or anger from other drivers.

I was holding 46.7 mpg, but I recently reduced my tire presssure from 40 to 37 psi to improve the ride and improve crosswind stability, and it dropped the mileage a bit. It is still great mileage, and I enjoy the car a lot more this way.