I'm in the process now of having my rear wheel warrantied. OEM wheel that came on new bike with WTB rim that started showing cracks around spoke holes. I've owned the bike for a year and a half when I noticed the problem. WTB lists a two year warranty on their site, and so I took it to the LBS I bought it from.
I don't know exactly how the warranty system worked (if it was through Cannondale or WTB) but there's a new WTB rim on the way and I'm paying nothing to have the wheel built back up.