In my experience, they’re not quite as sharp as a well-maintained steel knife, they’re absolutely inflexible (good for some kinds of knife but not so great in an astonishing number of types of knife), they’re much more prone to breaking than steel knives (specifically: they’ll usually shatter where a steel knife would only be slightly bent or nicked), and pretty much impossible to repair when they get nicked. Or to sharpen when they dull.
Apart from that, I’ve yet to come across a well-balanced ceramic knife, and they’re too light for my tastes.
On top of that: the cheap ones are fairly dull and tend to be badly made, decent ones are surprisingly expensive.
They can’t do anything a steel knife in the same price range doesn’t, are less robust and basically throw-away articles. What’s to like?
Tilman Ahr, Chef