I've read of a few studies regarding the safety and cleanliness of wooden vs. plastic cutting boards, and the wood ones fare much better than plastic when it's not possible to thoroughly sanitize the plastic ones (with, for instance, a commercial dishwasher). The plastic tends to develop grooves and scratches over time that hold stuff in, such that it cannot be completely cleaned by hand washing, and provides a very nice environment for the bacteria to multiply. Unfinished wood, on the other hand, naturally has some antimicrobial properties; bacteria do not survive long in contact with it.