I'm sure there are benefits, especially for racers, but I'm not a racer and I'm still carrying an extra 60 pounds or so around my waist. I will gain more of a performance increase by lightening and strengthening my own body. The 80/20 rule probably applies here. The 80% being the rider.

Sometimes its nice just to reward yourself with something just because you want it and can afford it. Still not sure if I'd go for a carbon bike, but I haven't ridden one yet either, so I can't really say.