When I found out the bearings had failed on my bike, I needed to decide what I wanted to do, and fast, so the bike wouldn't sit in the shop forever. I did a lot of reading on ceramic bearings in one evening, and found out there's very little scientific information and a bazillion opinions on ceramic bearings. We do know they're harder than steel bearings; that's quantifiable. It's also clear they're a lot more expensive. It also seems pretty undeniable that they're more brittle than steel, but I haven't seen any hard numbers showing that to be true, and I also don't pretend to know what's "tough enough" for a bearing to survive impacts without shattering or dimpling the races.
I've heard that "they'll wear longer", which seems plausible; they are harder, so it seems like wear particles might break off less frequently. But I've also heard they "don't last as long", which might be due to premature shattering, dimpling, or it may just be because people run them dry, without grease -- they're usually used by high-performance types that want them for their lighter weight and perceived lower friction.
So I decided I'd try them. If they do last longer, I may well never have to replace them again (I got 24,000 miles out of the original set). If it doesn't work, I'll just go back to steel, and I'll just have to get them replaced once in a while.
In a way this isn't a valid experiment, though, since in addition to going with ceramic, I'm pretty sure I upgraded them spec-wise too. The ones I chose are ABEC 5, C3 fit, and have Grade 5 balls, which is a pretty high-precision bearing, so it's probably not fair to compare to the originals (which I assume are mid-grade at best). Even the upgraded bearings are still cheaper than having another set put in down the road, however.