I bought the Cateye combo pack of a 3-LED white front light and a 3-LED red back light. I generally use them both on flash mode, but after reading this thread, I'll probably switch at least my red one to steady on trails. I definitely believe that blinking rather than steady is better at attracting attention.
I also have a Planet Bike Spok LED set on my helmet. The rear red Spok I leave blinking, but especially if I'm using the front Cateye in continuous "see" mode, I'll set the front Spok to flash, "be seen" mode. And for good measure, I've taken lately to wrapping a headlamp around my right wrist, which is more lumens for me, a backup in case something happens to the other lights, especially helpful in no-streetlights areas, and finally, a turn signal replicator if I signal right and flick my wrist up/back in rhythm.
Important safety tip--DO NOT USE A WHITE BLINKY ON THE BACK OF YOUR BIKE.
I read online (a long time ago) that there are international treaties requiring this, that white lights be on the front of vehicles, red lights on the rear and never the other way around. (You'll notice the next time a car goes into reverse mode, white lights generally light up on the back.) I don't know what the relationship is of those treaties to U.S. or Pennsylvania law, but if we follow this advice (and it seems bikers mostly do) it can avoid any situations like bjanaszek mentions.
I understand it is even required by certain european countries for some reason or another.
Yeah, I ride with a guy from Germany who told me that is the case there.
I think I read online somewhere that at least in Germany, flashing/blinking lights (maybe just certain colors like white) are reserved for police and emergency services.