it's not really the weight that matters to me.
it's the RIDE QUALITY, responsiveness and superior handling you get with a QUALITY CF bike.
of course the weight can make a difference when you ride 50 miles in 2.75 hours.
a cheap CF bike can be pure torture to ride long distances.

with all of the CF parts on the bike i bought weighed about 13lbs. a alloy bike would be close to 20lbs.
a high end steel bike that will have a $10K MSRP will weigh about 18lbs depending on the wheels.
a cheap steel department store bike will be close to 25lbs depending on how it's made, who makes it and what type of wheels are on it.

in the end it's a hobby and how much you want to spend and what you want to accomplish.
i can easily say you spent way more for you new performance car than i had in my original N96 V21 V25 striped 72 hemi road runner and the truck and car i had at the time combined.