I have 2 PB superflash blinkies, side by side, attached to the back of my seat pack. I ride at night this time of the year as it is my only time to get out during the work week. Cars swerve way out of the lane to get away from me. I've read comments from some who say it looks like an emergency light in the distance. With two, I can set one to blink and one in steady mode.
In addition, I also wear a reflective vest with a battery-controlled LED light down the back, I have tires w/reflective rims, pedals with reflectors on both sides, reflectors on each wheel, and two headlights.
With lights, it is very important to see AND be seen. It doesn't guarantee no one will hit me (there's always the cell phone talker or drunk driver to be concerned about), but at least no one can claim in a court of law that I wasn't visible if they do.
Specialized Roubaix Expert
Surly Long Haul Trucker