ceramic ones!? NO! NO! NO! They're very dangerous indeed.

It's not due to them trapping anything, it's as they're too hard. the knife won't grip the surface, so can slide about very easily. this is not good. Plus, even if you don't hurt yourself, it will make a mess of the knive in no time. This is why large kitchens use colour coded plastic. Fodd saftey and finger saftey.