weight mostly matters when you have to carry the bike up stairs and through turnstiles etc. If you are thinking of trying out carbon also consider some of the pre monocoque bikes: usually aluminum lugged. My Look rides more like a steel bike than my carbon KUOTA did.
One is smooth with a progressive spring, the other was stiff, twitchy and tightly sprung. The KUOTA was faster- and lighter- but also too much bike for my skills to really use. The Look feels and rides better for everyday use.