I have a kitchen knife that is ceramic. I have had it a year now and it is still super sharp. The down side is the blade is extremely brittle and it is not recommended to be used for chopping or cutting hard objects. It works great on slicing oranges but whittling wood might chip the blade.
I have one of the kitchen knives and it chipped in a few spots. I gave one to my mom and she broke it in half trying to open a can cuz they said it would cut metal on tv. I just think it's a novelty thing some clown came up with to make a buck.