Well, here at least are things labeled studies:
Daytime Running Lights: The Studies
Generally in favor of DRLs from a safety standpoint, maybe %10 reduction in crashes, $3/year to operate (in 1995 gasoline dollars ($0.75/gallon), times 120million drivers though), and a "statistically insignificant" 4% increase in motorcycle crashes
Edit, and a few noticeable increases in pedestrian/pedacycle collisions (boo!)