After work tonight I took a ~6 mile ride, which reinforced why it's prudent to wear bright clothing, have reflectors, and lights on your bike.
My ride was on the Schuykill River Trail between Miquon and Shawmont and by the time I got there it was dusk. There was some group run going on so that trail was crowded. A lot of runners were wearing dark clothing and as it got near 7:00 PM they got increasingly hard to see. Those wearing a safety yellow/green shirt were a lot more visible.
Likewise, only about half the other cyclists had lights and many of them didn't have any kind of reflectors.
Something the younger folks need to be aware of is that while you may be able to see just fine around dusk, those of us over 40 often start losing our night vision. (I noticed mine starting to go when I was 35.)
When I got back into cycling this summer I picked up these lights. They are cheap and at least in dry weather, work well. I put a set on my daughter's bike and with the rear set to alternately light one of the three LEDs, I was able to see her from over 200 yards away.
I also encourage the use of reflectors. Yeah, they're uncool. They are less uncool than getting hit by a car or another cyclist because they couldn't see you. Incidentally, I tested the supposedly-reflective sidewall lettering on my Bontrager H2 tires after getting home and was not impressed.
Finally, brightly colored clothes help make you more visible. I wore a bright orange Champion Powertrain T-shirt and I also have one in "reflector green." These shirts are lightweight, wick away moisture, and dry quickly. I have a few others in more subdued colors that I wear in the woods or in colder weather as a base layer, so they are multi-purpose.