It seems to me like no major manufacturers are using kevlar as a reinforcement. I ride a Look KG86 which has kevlar reinforcement but they don't do that anymore. I did read (somewhere?) that it has good shock/vibration absorbing properties, which makes me think about using a couple plies in the seatstays and seat tube. I'm in the process of research and design for my own composite frame and I'm not sure if the kevlar will really be worth the bother. I've also read that it's a lot harder to wet out compared to carbon.