I have to admit that I do put mine (about 12" in diameter & 1" thick) in the dishwasher occasionally, & it has not warped, but maybe I've just been lucky (also I don't use the heated drying cycle on my dishwasher). It's an easy cleanup with soap & water. Probably the best kitchen buy I have ever made -- definitely get one. Since getting mine, I've bought them for four other people & am trying to find one for a fifth (the store that carried them in Chinatown here no longer does).
This might help http://query.nytimes.com/gst/fullpage...
"quote" The cutting board has been certified by the National Sanitation Foundation, which tests a product's resistance to bacteria growth as well as its durability. If you do manage to mark the board up, however, you can simply use sandpaper to rub its surface until it is smooth again. To clean, scrub with soap and water; putting it in a dishwasher is not recommended, as the rubber could warp.