There is an advantage to SOME carbon fiber parts. The more money you spend, the lighter they get. Some carbon parts are actually heavier than their aluminum counterparts. Some parts, such as a carbon fiber seatpost, or carbon forks, will provide a bit of suppleness to an all aluminum frame and can make a big difference in comfort levels. The seatpost in particular can be a really noticable change. However if you want to really shed grams with items like handlebars, be prepared to spend upwards of 5 to 10 dollars per gram. For me that's just silly. I always seem to buy the parts that fall just short of depreciating gains.