Properly done, it's a good thing. I own a Serotta Ottrott, which is a carbon/ti hybrid bike. It could very well be the finest bike in the world. It has a ti head tube, seat tube and chainstays, while the seatstays, top and down tubes are carbon, along with the fork. This frame takes the "carbon seatstays and fork" thing to the next level, but it shows what can be done with a multi-material bike. While some may think that carbon is the best material for bike frames, The Serotta Ottrott uses the best material for each tube on the bike. It has the durability and light, springy feel of a great ti bike, but the carbon top and down tubes add ridgidity and vibration dampening, while the carbon seat stays do absorb road chatter and provide some rear vertical flex while keeping things tight and stiff in the horizontal plane. Steel frame purists may shudder at the thought of carbon seat stays on a steel frame, but let's face it- using different materials for different tasks can be a good idea. Would you ride a wheelset made of just one material? Many of the best wheels uses carbon, aluminum, steel and maybe even ceramic in their construction. It's just good engineering!