PROS:
1.) Ceramic Knives don't leave microscopic bits of metal in your food .... which causes your apples to turn brown and lettuce to wilt after cutting them.
2.) Ceramic Knives are harder then metal and don't need to be resharpened as often.
CONS:
1.) They are expensive.
2.) Lack flexibility so you can't bend them like a fillet knife.
3.) Not malleable/shock resistant like traditional stainless steel knives. If you drop it on the ground it will shatter like glass.
4.) Require Diamond tools to sharpen.
Basically, its an ideal knife for anyone pursuing a vegetarian life style or anyone that prepares sushi.
metal tools don't leave metal on your food, but contact with metal does speed up oxidation.
ceramic knives hardly ever require sharpening; most will go for a lifetime without ever needing it (seriously), but in case of chipping there is a sharpening service offered.
ceramic knives are a blade made of .. ceramic. hardness nearing that of diamond, they cut without ever going blunt; however, they need to be made sharp in the first place. kyocera aren't really that sharp, if you want sharp you need to get the even more expensive and delicate Kyotop (same brand, different set), which are also the only ones to have a proper tip (others have blunt tip).
ceramic is also fragile as ..well .. ceramic. it breaks if you bend it, drop it, or try to cut through a bone. they aren't meant to replace knives, they are meant to be an addition to a chef's set. when they do cut however, they cut splendidly .. and forever.
btw, the basic kyocera can be found on the internetz for £5-15, there's always too many in stock going on sales.
edit: why would i ever want a ceramic knife?
if you work with food and specifically, if you slice tomatoes ..
tomatoes' skin is a very tiny film of an incredible hard substance; you don't see it, but each time you slice one your blade goes severely more dull. this doesn't happen with ceramic knives, as they are substantially harder than the poor tomato (steel isn't).
so, if you cut tomatoes on a regular basis, it's totally worth it to spend $20 on a knife kept for that sole purpose, it makes the work so much faster.