According to Linda Stradley, author of What’s Cooking America: “Research has shown that bacteria, such as the salmonella often found on raw chicken, will thrive and multiply if not removed from plastic boards (because germs that cause food poisoning can hide out in the knife-scarred nooks and crannies that develop on the surface of a plastic cutting board).
“Hand scrubbing with hot water and soap can clear microbes from the surface of new or used wooden cutting boards and new plastic ones, but knife-scarred plastic boards are resistant to decontamination by hand washing.
“On wood boards, whether they are new or have been used for years, the bacteria dies off within three minutes. Researchers theorize that the porous surface of the wood surface of the wooden boards deprives the bacteria of water, causing them to die.”
Not convinced? Check out this study from UC Davis: http://faculty.vetmed.ucdavis.edu/faculty/docliver/Research/cuttingboard.htm