They work in saws of course. But, they don't seem to be really well suited to a harsh environment. For instance, if you have a saw that is eating dust, or fines, the ceramics seem not to be able to handle that as well as a steel bearing. I guess you could say that they are a bit more fragile. Maybe?
And.....in all fairness. This is just me parroting things I've been told by guys that I consider more experienced in all things saw related than me. I've never installed, nor do I plan to ever install a ceramic bearing in a saw engine.