Chris King announced their first ceramic bearing option in August 2011 with the R45 road hubs. As of December 1, they’re now offering ceramic bearings on all of their ISO mountain bike hubs.
The Santa Cruz Syndicate team has been race testing them on the World Cup DH Circuit (they get all the best toys, don’t they?). Benefits are that they’re lighter, stronger and rounder than steel balls. They produce their own ceramic bearings in house and even suggest running them with minimal silicone grease for “ultimate race day performance.” That said, there’s no appreciable weight savings, just smoothness improvements, and look for about a $80 upcharge.
Unrelated but interesting, the PressFit bottom brackets they announced at Eurobike are still on schedule for Spring 2013 release. They are still finalizing the design and testing them to ensure they’ll hold up to expectations, but they’re close. What we do know now is they’ll use their angular contact bearings and grease purge system, which lets you adjust the bearing tension like their outboard threaded bottom bracket and flush the old grease out without removing it from the frame. So, you’re wearing them in and adjusting to take up play rather than wearing them out. We’re as anxious as you are to try them!