Happens almost every year on the DALMAC, too. I was lucky, people around me on one stretch were all getting tacks. They were little black carpet-style tacks, so there was no way you could see them on the black road surface.

I don't know if I just managed to miss them, or if the heavy tires I was using saved me some trouble.

That stretch of road had been clear a couple hours before, so someone driving during the ride (and amongst the riders) must've thrown them out a window along several hundred yards.