Ed, Mad Dog makes a line of ceramic knives, the Mirage-X's which are probably the best out there right now.
They can be sharpened to slice well but they don't push cut at all and they chip out very easy compared to a steel knife. They are also not warrentied for breakage after dropping and are also much weaker laterally of course and thus tend to be made rather thick to compensate for this.
On the plus side they go a long time between sharpenings and they are not that difficult to sharpen. And of course the knife itself cannot be picked up on a metal detector which may be of use to some.
Mad Dog's forum on knifeforums.com has much more information including detailed reports by owners.
-Cliff