Ceramic knives are actually made from zirconium oxide ceramic, which the marketing materials of ceramic knife makers claim is the second hardest substance in the world after diamonds.
Ceramic knives are chic right now among fancy chefs because they really never get dull (need sharpening after 5 years as opposed to every 6 months) and because supposedly they do not impart a taste to the food that they cut. That seems to be a fairly obscure point unless one can really detect a taste imparted by a knife, I assume cooking of food destroys most of these odors. But it is a nice logical jump because ceramic knives are big in Japan. Japanese people eat a lot of sushi (I assume) and sushi is not cooked, therefore there might be a legitimate concern about steel knives adding a nasty flavor. Some of the iron chefs use ceramic knives. I noticed this because certain varieties of ceramic knives have a cool milky white cartilage look to them, and I first saw those in the hands of someone during the eggplant battle.
To prove their further bigness in Japan, William Gibson has mentioned ceramic knives in at least one of his novels, off the top of the dome I can remember a ceramic switchblade in either Virtual Light, Idoru or All Tomorrows Parties. They do have a cool cyberpunky quality especially considering their possible non-detectability by metal detectors and their exceptional sharpness.
However Gibson is probably wrong about the idea of lots of ceramic switchblades floating around because ceramic is really only suited for kitchen knives, utility knives and combat knives are not made out of ceramic because although they would be sharp as hell they wouldn't have a lot of lateral strength, and therefore could not be used to pry or jimmy without shattering.